diff --git a/codes/csharp/chapter_array_and_linkedlist/Array.cs b/codes/csharp/chapter_array_and_linkedlist/array.cs
similarity index 99%
rename from codes/csharp/chapter_array_and_linkedlist/Array.cs
rename to codes/csharp/chapter_array_and_linkedlist/array.cs
index cc6b79dd4..95479574f 100644
--- a/codes/csharp/chapter_array_and_linkedlist/Array.cs
+++ b/codes/csharp/chapter_array_and_linkedlist/array.cs
@@ -1,4 +1,4 @@
-// File: Array.cs
+// File: array.cs
// Created Time: 2022-12-14
// Author: mingXta (1195669834@qq.com)
@@ -134,4 +134,4 @@ namespace hello_algo.chapter_array_and_linkedlist
Console.WriteLine("在 nums 中查找元素 3 ,得到索引 = " + index);
}
}
-}
\ No newline at end of file
+}
diff --git a/codes/csharp/chapter_array_and_linkedlist/LinkedList.cs b/codes/csharp/chapter_array_and_linkedlist/linked_list.cs
similarity index 90%
rename from codes/csharp/chapter_array_and_linkedlist/LinkedList.cs
rename to codes/csharp/chapter_array_and_linkedlist/linked_list.cs
index 46b87a624..d700a5ae7 100644
--- a/codes/csharp/chapter_array_and_linkedlist/LinkedList.cs
+++ b/codes/csharp/chapter_array_and_linkedlist/linked_list.cs
@@ -1,4 +1,4 @@
-// File: LinkedList.cs
+// File: linked_list.cs
// Created Time: 2022-12-16
// Author: mingXta (1195669834@qq.com)
@@ -7,14 +7,14 @@ using NUnit.Framework;
namespace hello_algo.chapter_array_and_linkedlist
{
- public class LinkedList
+ public class linked_list
{
///
/// 在链表的结点 n0 之后插入结点 P
///
public static void Insert(ListNode n0, ListNode P)
{
- ListNode n1 = n0.next;
+ ListNode? n1 = n0.next;
n0.next = P;
P.next = n1;
}
@@ -28,14 +28,14 @@ namespace hello_algo.chapter_array_and_linkedlist
return;
// n0 -> P -> n1
ListNode P = n0.next;
- ListNode n1 = P.next;
+ ListNode? n1 = P.next;
n0.next = n1;
}
///
/// 访问链表中索引为 index 的结点
///
- public static ListNode Access(ListNode head, int index)
+ public static ListNode? Access(ListNode head, int index)
{
for (int i = 0; i < index; i++)
{
@@ -89,12 +89,12 @@ namespace hello_algo.chapter_array_and_linkedlist
Console.WriteLine($"删除结点后的链表为{n0}");
// 访问结点
- ListNode node = Access(n0, 3);
- Console.WriteLine($"链表中索引 3 处的结点的值 = {node.val}");
+ ListNode? node = Access(n0, 3);
+ Console.WriteLine($"链表中索引 3 处的结点的值 = {node?.val}");
// 查找结点
int index = Find(n0, 2);
Console.WriteLine($"链表中值为 2 的结点的索引 = {index}");
}
}
-}
\ No newline at end of file
+}
diff --git a/codes/csharp/chapter_array_and_linkedlist/list.cs b/codes/csharp/chapter_array_and_linkedlist/list.cs
new file mode 100644
index 000000000..87bb2f2a4
--- /dev/null
+++ b/codes/csharp/chapter_array_and_linkedlist/list.cs
@@ -0,0 +1,75 @@
+/**
+ * File: list.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_array_and_linkedlist
+{
+ public class list
+ {
+ [Test]
+ public void Test()
+ {
+
+ /* 初始化列表 */
+ // 注意数组的元素类型是 int[] 的包装类 int[]
+ int[] numbers = new int[] { 1, 3, 2, 5, 4 };
+ List list = numbers.ToList();
+ Console.WriteLine("列表 list = " + string.Join(",",list));
+
+ /* 访问元素 */
+ int num = list[1];
+ Console.WriteLine("访问索引 1 处的元素,得到 num = " + num);
+
+ /* 更新元素 */
+ list[1]=0;
+ Console.WriteLine("将索引 1 处的元素更新为 0 ,得到 list = " + string.Join(",", list));
+
+ /* 清空列表 */
+ list.Clear();
+ Console.WriteLine("清空列表后 list = " + string.Join(",", list));
+
+ /* 尾部添加元素 */
+ list.Add(1);
+ list.Add(3);
+ list.Add(2);
+ list.Add(5);
+ list.Add(4);
+ Console.WriteLine("添加元素后 list = " + string.Join(",", list));
+
+ /* 中间插入元素 */
+ list.Insert(3, 6);
+ Console.WriteLine("在索引 3 处插入数字 6 ,得到 list = " + string.Join(",", list));
+
+ /* 删除元素 */
+ list.RemoveAt(3);
+ Console.WriteLine("删除索引 3 处的元素,得到 list = " + string.Join(",", list));
+
+ /* 通过索引遍历列表 */
+ int count = 0;
+ for (int i = 0; i < list.Count(); i++)
+ {
+ count++;
+ }
+
+ /* 直接遍历列表元素 */
+ count = 0;
+ foreach (int n in list)
+ {
+ count++;
+ }
+
+ /* 拼接两个列表 */
+ List list1 = new() { 6, 8, 7, 10, 9 };
+ list.AddRange(list1);
+ Console.WriteLine("将列表 list1 拼接到 list 之后,得到 list = " + string.Join(",", list));
+
+ /* 排序列表 */
+ list.Sort(); // 排序后,列表元素从小到大排列
+ Console.WriteLine("排序列表后 list = " + string.Join(",", list));
+ }
+ }
+}
diff --git a/codes/csharp/chapter_array_and_linkedlist/my_list.cs b/codes/csharp/chapter_array_and_linkedlist/my_list.cs
new file mode 100644
index 000000000..327180625
--- /dev/null
+++ b/codes/csharp/chapter_array_and_linkedlist/my_list.cs
@@ -0,0 +1,164 @@
+/**
+ * File: my_list.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_array_and_linkedlist
+{
+ class MyList
+ {
+ private int[] nums; // 数组(存储列表元素)
+ private int capacity = 10; // 列表容量
+ private int size = 0; // 列表长度(即当前元素数量)
+ private int extendRatio = 2; // 每次列表扩容的倍数
+
+ /* 构造函数 */
+ public MyList()
+ {
+ nums = new int[capacity];
+ }
+
+ /* 获取列表长度(即当前元素数量)*/
+ public int Size()
+ {
+ return size;
+ }
+
+ /* 获取列表容量 */
+ public int Capacity()
+ {
+ return capacity;
+ }
+
+ /* 访问元素 */
+ public int Get(int index)
+ {
+ // 索引如果越界则抛出异常,下同
+ if (index >= size)
+ throw new IndexOutOfRangeException("索引越界");
+ return nums[index];
+ }
+
+ /* 更新元素 */
+ public void Set(int index, int num)
+ {
+ if (index >= size)
+ throw new IndexOutOfRangeException("索引越界");
+ nums[index] = num;
+ }
+
+ /* 尾部添加元素 */
+ public void Add(int num)
+ {
+ // 元素数量超出容量时,触发扩容机制
+ if (size == Capacity())
+ ExtendCapacity();
+ nums[size] = num;
+ // 更新元素数量
+ size++;
+ }
+
+ /* 中间插入元素 */
+ public void Insert(int index, int num)
+ {
+ if (index >= size)
+ throw new IndexOutOfRangeException("索引越界");
+ // 元素数量超出容量时,触发扩容机制
+ if (size == Capacity())
+ ExtendCapacity();
+ // 将索引 index 以及之后的元素都向后移动一位
+ for (int j = size - 1; j >= index; j--)
+ {
+ nums[j + 1] = nums[j];
+ }
+ nums[index] = num;
+ // 更新元素数量
+ size++;
+ }
+
+ /* 删除元素 */
+ public int Remove(int index)
+ {
+ if (index >= size)
+ throw new IndexOutOfRangeException("索引越界");
+ int num = nums[index];
+ // 将索引 index 之后的元素都向前移动一位
+ for (int j = index; j < size - 1; j++)
+ {
+ nums[j] = nums[j + 1];
+ }
+ // 更新元素数量
+ size--;
+ // 返回被删除元素
+ return num;
+ }
+
+ /* 列表扩容 */
+ public void ExtendCapacity()
+ {
+ // 新建一个长度为 size 的数组,并将原数组拷贝到新数组
+ System.Array.Resize(ref nums, Capacity() * extendRatio);
+ // 更新列表容量
+ capacity = nums.Length;
+ }
+
+ /* 将列表转换为数组 */
+ public int[] ToArray()
+ {
+ int size = Size();
+ // 仅转换有效长度范围内的列表元素
+ int[] nums = new int[size];
+ for (int i = 0; i < size; i++)
+ {
+ nums[i] = Get(i);
+ }
+ return nums;
+ }
+ }
+
+ public class my_list
+ {
+ [Test]
+ public void Test()
+ {
+ /* 初始化列表 */
+ MyList list = new MyList();
+ /* 尾部添加元素 */
+ list.Add(1);
+ list.Add(3);
+ list.Add(2);
+ list.Add(5);
+ list.Add(4);
+ Console.WriteLine("列表 list = " + string.Join(",", list.ToArray()) +
+ " ,容量 = " + list.Capacity() + " ,长度 = " + list.Size());
+
+ /* 中间插入元素 */
+ list.Insert(3, 6);
+ Console.WriteLine("在索引 3 处插入数字 6 ,得到 list = " + string.Join(",", list.ToArray()));
+
+ /* 删除元素 */
+ list.Remove(3);
+ Console.WriteLine("删除索引 3 处的元素,得到 list = " + string.Join(",", list.ToArray()));
+
+ /* 访问元素 */
+ int num = list.Get(1);
+ Console.WriteLine("访问索引 1 处的元素,得到 num = " + num);
+
+ /* 更新元素 */
+ list.Set(1, 0);
+ Console.WriteLine("将索引 1 处的元素更新为 0 ,得到 list = " + string.Join(",", list.ToArray()));
+
+ /* 测试扩容机制 */
+ for (int i = 0; i < 10; i++)
+ {
+ // 在 i = 5 时,列表长度将超出列表容量,此时触发扩容机制
+ list.Add(i);
+ }
+ Console.WriteLine("扩容后的列表 list = " + string.Join(",", list.ToArray()) +
+ " ,容量 = " + list.Capacity() + " ,长度 = " + list.Size());
+ }
+ }
+}
diff --git a/codes/csharp/chapter_computational_complexity/leetcode_two_sum.cs b/codes/csharp/chapter_computational_complexity/leetcode_two_sum.cs
new file mode 100644
index 000000000..6d45f99b3
--- /dev/null
+++ b/codes/csharp/chapter_computational_complexity/leetcode_two_sum.cs
@@ -0,0 +1,69 @@
+/**
+ * File: leetcode_two_sum.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_computational_complexity
+{
+ class SolutionBruteForce
+ {
+ public int[] twoSum(int[] nums, int target)
+ {
+ int size = nums.Length;
+ // 两层循环,时间复杂度 O(n^2)
+ for (int i = 0; i < size - 1; i++)
+ {
+ for (int j = i + 1; j < size; j++)
+ {
+ if (nums[i] + nums[j] == target)
+ return new int[] { i, j };
+ }
+ }
+ return new int[0];
+ }
+ }
+
+ class SolutionHashMap
+ {
+ public int[] twoSum(int[] nums, int target)
+ {
+ int size = nums.Length;
+ // 辅助哈希表,空间复杂度 O(n)
+ Dictionary dic = new();
+ // 单层循环,时间复杂度 O(n)
+ for (int i = 0; i < size; i++)
+ {
+ if (dic.ContainsKey(target - nums[i]))
+ {
+ return new int[] { dic[target - nums[i]], i };
+ }
+ dic.Add(nums[i], i);
+ }
+ return new int[0];
+ }
+ }
+
+ public class leetcode_two_sum
+ {
+ [Test]
+ public void Test()
+ {
+ // ======= Test Case =======
+ int[] nums = { 2, 7, 11, 15 };
+ int target = 9;
+
+ // ====== Driver Code ======
+ // 方法一
+ SolutionBruteForce slt1 = new SolutionBruteForce();
+ int[] res = slt1.twoSum(nums, target);
+ Console.WriteLine("方法一 res = " + string.Join(",", res));
+ // 方法二
+ SolutionHashMap slt2 = new SolutionHashMap();
+ res = slt2.twoSum(nums, target);
+ Console.WriteLine("方法二 res = " + string.Join(",", res));
+ }
+ }
+}
diff --git a/codes/csharp/chapter_computational_complexity/space_complexity.cs b/codes/csharp/chapter_computational_complexity/space_complexity.cs
new file mode 100644
index 000000000..c534c81b2
--- /dev/null
+++ b/codes/csharp/chapter_computational_complexity/space_complexity.cs
@@ -0,0 +1,122 @@
+/**
+ * File: space_complexity.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_computational_complexity
+{
+ public class space_complexity
+ {
+ /* 函数 */
+ static int function()
+ {
+ // do something
+ return 0;
+ }
+
+ /* 常数阶 */
+ static void constant(int n)
+ {
+ // 常量、变量、对象占用 O(1) 空间
+ int a = 0;
+ int b = 0;
+ int[] nums = new int[10000];
+ ListNode node = new ListNode(0);
+ // 循环中的变量占用 O(1) 空间
+ for (int i = 0; i < n; i++)
+ {
+ int c = 0;
+ }
+ // 循环中的函数占用 O(1) 空间
+ for (int i = 0; i < n; i++)
+ {
+ function();
+ }
+ }
+
+ /* 线性阶 */
+ static void linear(int n)
+ {
+ // 长度为 n 的数组占用 O(n) 空间
+ int[] nums = new int[n];
+ // 长度为 n 的列表占用 O(n) 空间
+ List nodes = new();
+ for (int i = 0; i < n; i++)
+ {
+ nodes.Add(new ListNode(i));
+ }
+ // 长度为 n 的哈希表占用 O(n) 空间
+ Dictionary map = new();
+ for (int i = 0; i < n; i++)
+ {
+ map.Add(i, i.ToString());
+ }
+ }
+
+ /* 线性阶(递归实现) */
+ static void linearRecur(int n)
+ {
+ Console.WriteLine("递归 n = " + n);
+ if (n == 1) return;
+ linearRecur(n - 1);
+ }
+
+ /* 平方阶 */
+ static void quadratic(int n)
+ {
+ // 矩阵占用 O(n^2) 空间
+ int[,] numMatrix = new int[n, n];
+ // 二维列表占用 O(n^2) 空间
+ List> numList = new();
+ for (int i = 0; i < n; i++)
+ {
+ List tmp = new();
+ for (int j = 0; j < n; j++)
+ {
+ tmp.Add(0);
+ }
+ numList.Add(tmp);
+ }
+ }
+
+ /* 平方阶(递归实现) */
+ static int quadraticRecur(int n)
+ {
+ if (n <= 0) return 0;
+ int[] nums = new int[n];
+ Console.WriteLine("递归 n = " + n + " 中的 nums 长度 = " + nums.Length);
+ return quadraticRecur(n - 1);
+ }
+
+ /* 指数阶(建立满二叉树) */
+ static TreeNode? buildTree(int n)
+ {
+ if (n == 0) return null;
+ TreeNode root = new TreeNode(0);
+ root.left = buildTree(n - 1);
+ root.right = buildTree(n - 1);
+ return root;
+ }
+
+ [Test]
+ public void Test()
+ {
+ int n = 5;
+ // 常数阶
+ constant(n);
+ // 线性阶
+ linear(n);
+ linearRecur(n);
+ // 平方阶
+ quadratic(n);
+ quadraticRecur(n);
+ // 指数阶
+ TreeNode? root = buildTree(n);
+ PrintUtil.PrintTree(root);
+ }
+ }
+}
diff --git a/codes/csharp/chapter_computational_complexity/time_complexity.cs b/codes/csharp/chapter_computational_complexity/time_complexity.cs
new file mode 100644
index 000000000..2bbd01763
--- /dev/null
+++ b/codes/csharp/chapter_computational_complexity/time_complexity.cs
@@ -0,0 +1,232 @@
+/**
+ * File: time_complexity.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_computational_complexity
+{
+ public class time_complexity
+ {
+ void algorithm(int n)
+ {
+ int a = 1; // +0(技巧 1)
+ a = a + n; // +0(技巧 1)
+ // +n(技巧 2)
+ for (int i = 0; i < 5 * n + 1; i++)
+ {
+ Console.WriteLine(0);
+ }
+ // +n*n(技巧 3)
+ for (int i = 0; i < 2 * n; i++)
+ {
+ for (int j = 0; j < n + 1; j++)
+ {
+ Console.WriteLine(0);
+ }
+ }
+ }
+
+ // 算法 A 时间复杂度:常数阶
+ void algorithm_A(int n)
+ {
+ Console.WriteLine(0);
+ }
+ // 算法 B 时间复杂度:线性阶
+ void algorithm_B(int n)
+ {
+ for (int i = 0; i < n; i++)
+ {
+ Console.WriteLine(0);
+ }
+ }
+ // 算法 C 时间复杂度:常数阶
+ void algorithm_C(int n)
+ {
+ for (int i = 0; i < 1000000; i++)
+ {
+ Console.WriteLine(0);
+ }
+ }
+
+ /* 常数阶 */
+ static int constant(int n)
+ {
+ int count = 0;
+ int size = 100000;
+ for (int i = 0; i < size; i++)
+ count++;
+ return count;
+ }
+
+ /* 线性阶 */
+ static int linear(int n)
+ {
+ int count = 0;
+ for (int i = 0; i < n; i++)
+ count++;
+ return count;
+ }
+
+ /* 线性阶(遍历数组) */
+ static int arrayTraversal(int[] nums)
+ {
+ int count = 0;
+ // 循环次数与数组长度成正比
+ foreach (int num in nums)
+ {
+ count++;
+ }
+ return count;
+ }
+
+ /* 平方阶 */
+ static int quadratic(int n)
+ {
+ int count = 0;
+ // 循环次数与数组长度成平方关系
+ for (int i = 0; i < n; i++)
+ {
+ for (int j = 0; j < n; j++)
+ {
+ count++;
+ }
+ }
+ return count;
+ }
+
+ /* 平方阶(冒泡排序) */
+ static int bubbleSort(int[] nums)
+ {
+ int count = 0; // 计数器
+ // 外循环:待排序元素数量为 n-1, n-2, ..., 1
+ for (int i = nums.Length - 1; i > 0; i--)
+ {
+ // 内循环:冒泡操作
+ for (int j = 0; j < i; j++)
+ {
+ if (nums[j] > nums[j + 1])
+ {
+ // 交换 nums[j] 与 nums[j + 1]
+ int tmp = nums[j];
+ nums[j] = nums[j + 1];
+ nums[j + 1] = tmp;
+ count += 3; // 元素交换包含 3 个单元操作
+ }
+ }
+ }
+ return count;
+ }
+
+ /* 指数阶(循环实现) */
+ static int exponential(int n)
+ {
+ int count = 0, bas = 1;
+ // cell 每轮一分为二,形成数列 1, 2, 4, 8, ..., 2^(n-1)
+ for (int i = 0; i < n; i++)
+ {
+ for (int j = 0; j < bas; j++)
+ {
+ count++;
+ }
+ bas *= 2;
+ }
+ // count = 1 + 2 + 4 + 8 + .. + 2^(n-1) = 2^n - 1
+ return count;
+ }
+
+ /* 指数阶(递归实现) */
+ static int expRecur(int n)
+ {
+ if (n == 1) return 1;
+ return expRecur(n - 1) + expRecur(n - 1) + 1;
+ }
+
+ /* 对数阶(循环实现) */
+ static int logarithmic(float n)
+ {
+ int count = 0;
+ while (n > 1)
+ {
+ n = n / 2;
+ count++;
+ }
+ return count;
+ }
+
+ /* 对数阶(递归实现) */
+ static int logRecur(float n)
+ {
+ if (n <= 1) return 0;
+ return logRecur(n / 2) + 1;
+ }
+
+ /* 线性对数阶 */
+ static int linearLogRecur(float n)
+ {
+ if (n <= 1) return 1;
+ int count = linearLogRecur(n / 2) +
+ linearLogRecur(n / 2);
+ for (int i = 0; i < n; i++)
+ {
+ count++;
+ }
+ return count;
+ }
+
+ /* 阶乘阶(递归实现) */
+ static int factorialRecur(int n)
+ {
+ if (n == 0) return 1;
+ int count = 0;
+ // 从 1 个分裂出 n 个
+ for (int i = 0; i < n; i++)
+ {
+ count += factorialRecur(n - 1);
+ }
+ return count;
+ }
+
+ [Test]
+ public void Test()
+ {
+ // 可以修改 n 运行,体会一下各种复杂度的操作数量变化趋势
+ int n = 8;
+ Console.WriteLine("输入数据大小 n = " + n);
+
+ int count = constant(n);
+ Console.WriteLine("常数阶的计算操作数量 = " + count);
+
+ count = linear(n);
+ Console.WriteLine("线性阶的计算操作数量 = " + count);
+ count = arrayTraversal(new int[n]);
+ Console.WriteLine("线性阶(遍历数组)的计算操作数量 = " + count);
+
+ count = quadratic(n);
+ Console.WriteLine("平方阶的计算操作数量 = " + count);
+ int[] nums = new int[n];
+ for (int i = 0; i < n; i++)
+ nums[i] = n - i; // [n,n-1,...,2,1]
+ count = bubbleSort(nums);
+ Console.WriteLine("平方阶(冒泡排序)的计算操作数量 = " + count);
+
+ count = exponential(n);
+ Console.WriteLine("指数阶(循环实现)的计算操作数量 = " + count);
+ count = expRecur(n);
+ Console.WriteLine("指数阶(递归实现)的计算操作数量 = " + count);
+
+ count = logarithmic((float)n);
+ Console.WriteLine("对数阶(循环实现)的计算操作数量 = " + count);
+ count = logRecur((float)n);
+ Console.WriteLine("对数阶(递归实现)的计算操作数量 = " + count);
+
+ count = linearLogRecur((float)n);
+ Console.WriteLine("线性对数阶(递归实现)的计算操作数量 = " + count);
+
+ count = factorialRecur(n);
+ Console.WriteLine("阶乘阶(递归实现)的计算操作数量 = " + count);
+ }
+ }
+}
diff --git a/codes/csharp/chapter_computational_complexity/worst_best_time_complexity.cs b/codes/csharp/chapter_computational_complexity/worst_best_time_complexity.cs
new file mode 100644
index 000000000..9759cd584
--- /dev/null
+++ b/codes/csharp/chapter_computational_complexity/worst_best_time_complexity.cs
@@ -0,0 +1,61 @@
+/**
+ * File: worst_best_time_complexity.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_computational_complexity
+{
+ public class worst_best_time_complexity
+ {
+ /* 生成一个数组,元素为 { 1, 2, ..., n },顺序被打乱 */
+ static int[] randomNumbers(int n)
+ {
+ int[] nums = new int[n];
+ // 生成数组 nums = { 1, 2, 3, ..., n }
+ for (int i = 0; i < n; i++)
+ {
+ nums[i] = i + 1;
+ }
+
+ // 随机打乱数组元素
+ for (int i = 0; i < nums.Length; i++)
+ {
+ var index = new Random().Next(i, nums.Length);
+ var tmp = nums[i];
+ var ran = nums[index];
+ nums[i] = ran;
+ nums[index] = tmp;
+ }
+ return nums;
+ }
+
+ /* 查找数组 nums 中数字 1 所在索引 */
+ static int findOne(int[] nums)
+ {
+ for (int i = 0; i < nums.Length; i++)
+ {
+ if (nums[i] == 1)
+ return i;
+ }
+ return -1;
+ }
+
+
+ /* Driver Code */
+ [Test]
+ public void Test()
+ {
+ for (int i = 0; i < 10; i++)
+ {
+ int n = 100;
+ int[] nums = randomNumbers(n);
+ int index = findOne(nums);
+ Console.WriteLine("\n数组 [ 1, 2, ..., n ] 被打乱后 = " + string.Join(",", nums));
+ Console.WriteLine("数字 1 的索引为 " + index);
+ }
+ }
+ }
+}
diff --git a/codes/csharp/chapter_hashing/array_hash_map.cs b/codes/csharp/chapter_hashing/array_hash_map.cs
new file mode 100644
index 000000000..3320fa856
--- /dev/null
+++ b/codes/csharp/chapter_hashing/array_hash_map.cs
@@ -0,0 +1,164 @@
+/**
+ * File: array_hash_map.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_hashing
+{
+
+ /* 键值对 int->String */
+ class Entry
+ {
+ public int key;
+ public String val;
+ public Entry(int key, String val)
+ {
+ this.key = key;
+ this.val = val;
+ }
+ }
+
+ /* 基于数组简易实现的哈希表 */
+ class ArrayHashMap
+ {
+ private List bucket;
+ public ArrayHashMap()
+ {
+ // 初始化一个长度为 100 的桶(数组)
+ bucket = new ();
+ for (int i = 0; i < 100; i++)
+ {
+ bucket.Add(null);
+ }
+ }
+
+ /* 哈希函数 */
+ private int hashFunc(int key)
+ {
+ int index = key % 100;
+ return index;
+ }
+
+ /* 查询操作 */
+ public String? get(int key)
+ {
+ int index = hashFunc(key);
+ Entry? pair = bucket[index];
+ if (pair == null) return null;
+ return pair.val;
+ }
+
+ /* 添加操作 */
+ public void put(int key, String val)
+ {
+ Entry pair = new Entry(key, val);
+ int index = hashFunc(key);
+ bucket[index]=pair;
+ }
+
+ /* 删除操作 */
+ public void remove(int key)
+ {
+ int index = hashFunc(key);
+ // 置为 null ,代表删除
+ bucket[index]=null;
+ }
+
+ /* 获取所有键值对 */
+ public List entrySet()
+ {
+ List entrySet = new ();
+ foreach (Entry? pair in bucket)
+ {
+ if (pair != null)
+ entrySet.Add(pair);
+ }
+ return entrySet;
+ }
+
+ /* 获取所有键 */
+ public List keySet()
+ {
+ List keySet = new ();
+ foreach (Entry? pair in bucket)
+ {
+ if (pair != null)
+ keySet.Add(pair.key);
+ }
+ return keySet;
+ }
+
+ /* 获取所有值 */
+ public List valueSet()
+ {
+ List valueSet = new ();
+ foreach (Entry? pair in bucket)
+ {
+ if (pair != null)
+ valueSet.Add(pair.val);
+ }
+ return valueSet;
+ }
+
+ /* 打印哈希表 */
+ public void print()
+ {
+ foreach (Entry kv in entrySet())
+ {
+ Console.WriteLine(kv.key + " -> " + kv.val);
+ }
+ }
+ }
+
+
+ public class array_hash_map
+ {
+ [Test]
+ public void Test()
+ {
+ /* 初始化哈希表 */
+ ArrayHashMap map = new ArrayHashMap();
+
+ /* 添加操作 */
+ // 在哈希表中添加键值对 (key, value)
+ map.put(12836, "小哈");
+ map.put(15937, "小啰");
+ map.put(16750, "小算");
+ map.put(13276, "小法");
+ map.put(10583, "小鸭");
+ Console.WriteLine("\n添加完成后,哈希表为\nKey -> Value");
+ map.print();
+
+ /* 查询操作 */
+ // 向哈希表输入键 key ,得到值 value
+ String? name = map.get(15937);
+ Console.WriteLine("\n输入学号 15937 ,查询到姓名 " + name);
+
+ /* 删除操作 */
+ // 在哈希表中删除键值对 (key, value)
+ map.remove(10583);
+ Console.WriteLine("\n删除 10583 后,哈希表为\nKey -> Value");
+ map.print();
+
+ /* 遍历哈希表 */
+ Console.WriteLine("\n遍历键值对 Key->Value");
+ foreach (Entry kv in map.entrySet())
+ {
+ Console.WriteLine(kv.key + " -> " + kv.val);
+ }
+ Console.WriteLine("\n单独遍历键 Key");
+ foreach (int key in map.keySet())
+ {
+ Console.WriteLine(key);
+ }
+ Console.WriteLine("\n单独遍历值 Value");
+ foreach (String val in map.valueSet())
+ {
+ Console.WriteLine(val);
+ }
+ }
+ }
+}
\ No newline at end of file
diff --git a/codes/csharp/chapter_hashing/hash_map.cs b/codes/csharp/chapter_hashing/hash_map.cs
new file mode 100644
index 000000000..6afcc82c8
--- /dev/null
+++ b/codes/csharp/chapter_hashing/hash_map.cs
@@ -0,0 +1,57 @@
+
+/**
+ * File: hash_map.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_hashing
+{
+
+ public class hash_map {
+ [Test]
+ public void Test()
+ {
+ /* 初始化哈希表 */
+ Dictionary map = new ();
+
+ /* 添加操作 */
+ // 在哈希表中添加键值对 (key, value)
+ map.Add(12836, "小哈");
+ map.Add(15937, "小啰");
+ map.Add(16750, "小算");
+ map.Add(13276, "小法");
+ map.Add(10583, "小鸭");
+ Console.WriteLine("\n添加完成后,哈希表为\nKey -> Value");
+ PrintUtil.printHashMap(map);
+
+ /* 查询操作 */
+ // 向哈希表输入键 key ,得到值 value
+ String name = map[15937];
+ Console.WriteLine("\n输入学号 15937 ,查询到姓名 " + name);
+
+ /* 删除操作 */
+ // 在哈希表中删除键值对 (key, value)
+ map.Remove(10583);
+ Console.WriteLine("\n删除 10583 后,哈希表为\nKey -> Value");
+ PrintUtil.printHashMap(map);
+
+ /* 遍历哈希表 */
+ Console.WriteLine("\n遍历键值对 Key->Value");
+ foreach (var kv in map) {
+ Console.WriteLine(kv.Key + " -> " + kv.Value);
+ }
+ Console.WriteLine("\n单独遍历键 Key");
+ foreach (int key in map.Keys) {
+ Console.WriteLine(key);
+ }
+ Console.WriteLine("\n单独遍历值 Value");
+ foreach (String val in map.Values) {
+ Console.WriteLine(val);
+ }
+ }
+ }
+}
diff --git a/codes/csharp/chapter_searching/binary_search.cs b/codes/csharp/chapter_searching/binary_search.cs
new file mode 100644
index 000000000..1bf8a5b2f
--- /dev/null
+++ b/codes/csharp/chapter_searching/binary_search.cs
@@ -0,0 +1,68 @@
+/**
+ * File: binary_search.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_searching
+{
+ public class binary_search
+ {
+ /* 二分查找(双闭区间) */
+ static int binarySearch(int[] nums, int target)
+ {
+ // 初始化双闭区间 [0, n-1] ,即 i, j 分别指向数组首元素、尾元素
+ int i = 0, j = nums.Length - 1;
+ // 循环,当搜索区间为空时跳出(当 i > j 时为空)
+ while (i <= j)
+ {
+ int m = (i + j) / 2; // 计算中点索引 m
+ if (nums[m] < target) // 此情况说明 target 在区间 [m+1, j] 中
+ i = m + 1;
+ else if (nums[m] > target) // 此情况说明 target 在区间 [i, m-1] 中
+ j = m - 1;
+ else // 找到目标元素,返回其索引
+ return m;
+ }
+ // 未找到目标元素,返回 -1
+ return -1;
+ }
+
+ /* 二分查找(左闭右开) */
+ static int binarySearch1(int[] nums, int target)
+ {
+ // 初始化左闭右开 [0, n) ,即 i, j 分别指向数组首元素、尾元素+1
+ int i = 0, j = nums.Length;
+ // 循环,当搜索区间为空时跳出(当 i = j 时为空)
+ while (i < j)
+ {
+ int m = (i + j) / 2; // 计算中点索引 m
+ if (nums[m] < target) // 此情况说明 target 在区间 [m+1, j) 中
+ i = m + 1;
+ else if (nums[m] > target) // 此情况说明 target 在区间 [i, m) 中
+ j = m;
+ else // 找到目标元素,返回其索引
+ return m;
+ }
+ // 未找到目标元素,返回 -1
+ return -1;
+ }
+
+ [Test]
+ public void Test()
+ {
+ int target = 6;
+ int[] nums = { 1, 3, 6, 8, 12, 15, 23, 67, 70, 92 };
+
+ /* 二分查找(双闭区间) */
+ int index = binarySearch(nums, target);
+ Console.WriteLine("目标元素 6 的索引 = " + index);
+
+ /* 二分查找(左闭右开) */
+ index = binarySearch1(nums, target);
+ Console.WriteLine("目标元素 6 的索引 = " + index);
+ }
+ }
+}
diff --git a/codes/csharp/chapter_searching/hashing_search.cs b/codes/csharp/chapter_searching/hashing_search.cs
new file mode 100644
index 000000000..33d5fe9dc
--- /dev/null
+++ b/codes/csharp/chapter_searching/hashing_search.cs
@@ -0,0 +1,60 @@
+/**
+ * File: hashing_search.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_searching
+{
+ public class hashing_search
+ {
+ /* 哈希查找(数组) */
+ static int hashingSearch(Dictionary map, int target)
+ {
+ // 哈希表的 key: 目标元素,value: 索引
+ // 若哈希表中无此 key ,返回 -1
+ return map.GetValueOrDefault(target, -1);
+ }
+
+ /* 哈希查找(链表) */
+ static ListNode? hashingSearch1(Dictionary map, int target)
+ {
+
+ // 哈希表的 key: 目标结点值,value: 结点对象
+ // 若哈希表中无此 key ,返回 null
+ return map.GetValueOrDefault(target);
+ }
+
+ [Test]
+ public void Test()
+ {
+ int target = 3;
+
+ /* 哈希查找(数组) */
+ int[] nums = { 1, 5, 3, 2, 4, 7, 5, 9, 10, 8 };
+ // 初始化哈希表
+ Dictionary map = new();
+ for (int i = 0; i < nums.Length; i++)
+ {
+ map[nums[i]] = i; // key: 元素,value: 索引
+ }
+ int index = hashingSearch(map, target);
+ Console.WriteLine("目标元素 3 的索引 = " + index);
+
+ /* 哈希查找(链表) */
+ ListNode? head = ListNode.ArrToLinkedList(nums);
+ // 初始化哈希表
+ Dictionary map1 = new();
+ while (head != null)
+ {
+ map1[head.val] = head; // key: 结点值,value: 结点
+ head = head.next;
+ }
+ ListNode? node = hashingSearch1(map1, target);
+ Console.WriteLine("目标结点值 3 的对应结点对象为 " + node);
+ }
+ }
+}
diff --git a/codes/csharp/chapter_searching/linear_search.cs b/codes/csharp/chapter_searching/linear_search.cs
new file mode 100644
index 000000000..412eb37d3
--- /dev/null
+++ b/codes/csharp/chapter_searching/linear_search.cs
@@ -0,0 +1,59 @@
+/**
+ * File: linear_search.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_searching
+{
+ public class linear_search
+ {
+ /* 线性查找(数组) */
+ static int linearSearch(int[] nums, int target)
+ {
+ // 遍历数组
+ for (int i = 0; i < nums.Length; i++)
+ {
+ // 找到目标元素,返回其索引
+ if (nums[i] == target)
+ return i;
+ }
+ // 未找到目标元素,返回 -1
+ return -1;
+ }
+
+ /* 线性查找(链表) */
+ static ListNode? linearSearch(ListNode head, int target)
+ {
+ // 遍历链表
+ while (head != null)
+ {
+ // 找到目标结点,返回之
+ if (head.val == target)
+ return head;
+ head = head.next;
+ }
+ // 未找到目标结点,返回 null
+ return null;
+ }
+
+ [Test]
+ public void Test()
+ {
+ int target = 3;
+
+ /* 在数组中执行线性查找 */
+ int[] nums = { 1, 5, 3, 2, 4, 7, 5, 9, 10, 8 };
+ int index = linearSearch(nums, target);
+ Console.WriteLine("目标元素 3 的索引 = " + index);
+
+ /* 在链表中执行线性查找 */
+ ListNode head = ListNode.ArrToLinkedList(nums);
+ ListNode? node = linearSearch(head, target);
+ Console.WriteLine("目标结点值 3 的对应结点对象为 " + node);
+ }
+ }
+}
diff --git a/codes/csharp/chapter_sorting/bubble_sort.cs b/codes/csharp/chapter_sorting/bubble_sort.cs
new file mode 100644
index 000000000..b3304df04
--- /dev/null
+++ b/codes/csharp/chapter_sorting/bubble_sort.cs
@@ -0,0 +1,68 @@
+/**
+ * File: bubble_sort.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_sorting
+{
+ public class bubble_sort
+ {
+ /* 冒泡排序 */
+ static void bubbleSort(int[] nums)
+ {
+ // 外循环:待排序元素数量为 n-1, n-2, ..., 1
+ for (int i = nums.Length - 1; i > 0; i--)
+ {
+ // 内循环:冒泡操作
+ for (int j = 0; j < i; j++)
+ {
+ if (nums[j] > nums[j + 1])
+ {
+ // 交换 nums[j] 与 nums[j + 1]
+ int tmp = nums[j];
+ nums[j] = nums[j + 1];
+ nums[j + 1] = tmp;
+ }
+ }
+ }
+ }
+
+ /* 冒泡排序(标志优化)*/
+ static void bubbleSortWithFlag(int[] nums)
+ {
+ // 外循环:待排序元素数量为 n-1, n-2, ..., 1
+ for (int i = nums.Length - 1; i > 0; i--)
+ {
+ bool flag = false; // 初始化标志位
+ // 内循环:冒泡操作
+ for (int j = 0; j < i; j++)
+ {
+ if (nums[j] > nums[j + 1])
+ {
+ // 交换 nums[j] 与 nums[j + 1]
+ int tmp = nums[j];
+ nums[j] = nums[j + 1];
+ nums[j + 1] = tmp;
+ flag = true; // 记录交换元素
+ }
+ }
+ if (!flag) break; // 此轮冒泡未交换任何元素,直接跳出
+ }
+ }
+
+ [Test]
+ public void Test()
+ {
+ int[] nums = { 4, 1, 3, 1, 5, 2 };
+ bubbleSort(nums);
+ Console.WriteLine("冒泡排序完成后 nums = " + string.Join(",",nums));
+
+ int[] nums1 = { 4, 1, 3, 1, 5, 2 };
+ bubbleSortWithFlag(nums1);
+ Console.WriteLine("冒泡排序完成后 nums1 = " + string.Join(",", nums));
+ }
+ }
+}
diff --git a/codes/csharp/chapter_sorting/insertion_sort.cs b/codes/csharp/chapter_sorting/insertion_sort.cs
new file mode 100644
index 000000000..0f674c9fc
--- /dev/null
+++ b/codes/csharp/chapter_sorting/insertion_sort.cs
@@ -0,0 +1,38 @@
+/**
+ * File: insertion_sort.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_sorting
+{
+ public class insertion_sort
+ {
+ /* 插入排序 */
+ static void insertionSort(int[] nums)
+ {
+ // 外循环:base = nums[1], nums[2], ..., nums[n-1]
+ for (int i = 1; i < nums.Length; i++)
+ {
+ int bas = nums[i], j = i - 1;
+ // 内循环:将 base 插入到左边的正确位置
+ while (j >= 0 && nums[j] > bas)
+ {
+ nums[j + 1] = nums[j]; // 1. 将 nums[j] 向右移动一位
+ j--;
+ }
+ nums[j + 1] = bas; // 2. 将 base 赋值到正确位置
+ }
+ }
+
+ [Test]
+ public void Test()
+ {
+ int[] nums = { 4, 1, 3, 1, 5, 2 };
+ insertionSort(nums);
+ Console.WriteLine("插入排序完成后 nums = " + string.Join(",", nums));
+ }
+ }
+}
diff --git a/codes/csharp/chapter_sorting/merge_sort.cs b/codes/csharp/chapter_sorting/merge_sort.cs
new file mode 100644
index 000000000..04ac8acdd
--- /dev/null
+++ b/codes/csharp/chapter_sorting/merge_sort.cs
@@ -0,0 +1,65 @@
+/**
+ * File: merge_sort.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_sorting
+{
+ public class merge_sort
+ {
+ /**
+ * 合并左子数组和右子数组
+ * 左子数组区间 [left, mid]
+ * 右子数组区间 [mid + 1, right]
+ */
+ static void merge(int[] nums, int left, int mid, int right)
+ {
+ // 初始化辅助数组
+ int[] tmp = nums[left..(right + 1)];
+ // 左子数组的起始索引和结束索引
+ int leftStart = left - left, leftEnd = mid - left;
+ // 右子数组的起始索引和结束索引
+ int rightStart = mid + 1 - left, rightEnd = right - left;
+ // i, j 分别指向左子数组、右子数组的首元素
+ int i = leftStart, j = rightStart;
+ // 通过覆盖原数组 nums 来合并左子数组和右子数组
+ for (int k = left; k <= right; k++)
+ {
+ // 若“左子数组已全部合并完”,则选取右子数组元素,并且 j++
+ if (i > leftEnd)
+ nums[k] = tmp[j++];
+ // 否则,若“右子数组已全部合并完”或“左子数组元素 < 右子数组元素”,则选取左子数组元素,并且 i++
+ else if (j > rightEnd || tmp[i] <= tmp[j])
+ nums[k] = tmp[i++];
+ // 否则,若“左子数组元素 > 右子数组元素”,则选取右子数组元素,并且 j++
+ else
+ nums[k] = tmp[j++];
+ }
+ }
+
+ /* 归并排序 */
+ static void mergeSort(int[] nums, int left, int right)
+ {
+ // 终止条件
+ if (left >= right) return; // 当子数组长度为 1 时终止递归
+ // 划分阶段
+ int mid = (left + right) / 2; // 计算中点
+ mergeSort(nums, left, mid); // 递归左子数组
+ mergeSort(nums, mid + 1, right); // 递归右子数组
+ // 合并阶段
+ merge(nums, left, mid, right);
+ }
+
+ [Test]
+ public void Test()
+ {
+ /* 归并排序 */
+ int[] nums = { 7, 3, 2, 6, 0, 1, 5, 4 };
+ mergeSort(nums, 0, nums.Length - 1);
+ Console.WriteLine("归并排序完成后 nums = " + string.Join(",", nums));
+ }
+ }
+}
diff --git a/codes/csharp/chapter_sorting/quick_sort.cs b/codes/csharp/chapter_sorting/quick_sort.cs
new file mode 100644
index 000000000..020d4f342
--- /dev/null
+++ b/codes/csharp/chapter_sorting/quick_sort.cs
@@ -0,0 +1,183 @@
+/**
+ * File: quick_sort.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_sorting
+{
+ class QuickSort
+ {
+ /* 元素交换 */
+ static void swap(int[] nums, int i, int j)
+ {
+ int tmp = nums[i];
+ nums[i] = nums[j];
+ nums[j] = tmp;
+ }
+
+ /* 哨兵划分 */
+ static int partition(int[] nums, int left, int right)
+ {
+ // 以 nums[left] 作为基准数
+ int i = left, j = right;
+ while (i < j)
+ {
+ while (i < j && nums[j] >= nums[left])
+ j--; // 从右向左找首个小于基准数的元素
+ while (i < j && nums[i] <= nums[left])
+ i++; // 从左向右找首个大于基准数的元素
+ swap(nums, i, j); // 交换这两个元素
+ }
+ swap(nums, i, left); // 将基准数交换至两子数组的分界线
+ return i; // 返回基准数的索引
+ }
+
+ /* 快速排序 */
+ public static void quickSort(int[] nums, int left, int right)
+ {
+ // 子数组长度为 1 时终止递归
+ if (left >= right)
+ return;
+ // 哨兵划分
+ int pivot = partition(nums, left, right);
+ // 递归左子数组、右子数组
+ quickSort(nums, left, pivot - 1);
+ quickSort(nums, pivot + 1, right);
+ }
+ }
+
+ /* 快速排序类(中位基准数优化) */
+ class QuickSortMedian
+ {
+ /* 元素交换 */
+ static void swap(int[] nums, int i, int j)
+ {
+ int tmp = nums[i];
+ nums[i] = nums[j];
+ nums[j] = tmp;
+ }
+
+ /* 选取三个元素的中位数 */
+ static int medianThree(int[] nums, int left, int mid, int right)
+ {
+ // 使用了异或操作来简化代码
+ // 异或规则为 0 ^ 0 = 1 ^ 1 = 0, 0 ^ 1 = 1 ^ 0 = 1
+ if ((nums[left] > nums[mid]) ^ (nums[left] > nums[right]))
+ return left;
+ else if ((nums[mid] < nums[left]) ^ (nums[mid] < nums[right]))
+ return mid;
+ else
+ return right;
+ }
+
+ /* 哨兵划分(三数取中值) */
+ static int partition(int[] nums, int left, int right)
+ {
+ // 选取三个候选元素的中位数
+ int med = medianThree(nums, left, (left + right) / 2, right);
+ // 将中位数交换至数组最左端
+ swap(nums, left, med);
+ // 以 nums[left] 作为基准数
+ int i = left, j = right;
+ while (i < j)
+ {
+ while (i < j && nums[j] >= nums[left])
+ j--; // 从右向左找首个小于基准数的元素
+ while (i < j && nums[i] <= nums[left])
+ i++; // 从左向右找首个大于基准数的元素
+ swap(nums, i, j); // 交换这两个元素
+ }
+ swap(nums, i, left); // 将基准数交换至两子数组的分界线
+ return i; // 返回基准数的索引
+ }
+
+ /* 快速排序 */
+ public static void quickSort(int[] nums, int left, int right)
+ {
+ // 子数组长度为 1 时终止递归
+ if (left >= right)
+ return;
+ // 哨兵划分
+ int pivot = partition(nums, left, right);
+ // 递归左子数组、右子数组
+ quickSort(nums, left, pivot - 1);
+ quickSort(nums, pivot + 1, right);
+ }
+ }
+
+ /* 快速排序类(尾递归优化) */
+ class QuickSortTailCall
+ {
+ /* 元素交换 */
+ static void swap(int[] nums, int i, int j)
+ {
+ int tmp = nums[i];
+ nums[i] = nums[j];
+ nums[j] = tmp;
+ }
+
+ /* 哨兵划分 */
+ static int partition(int[] nums, int left, int right)
+ {
+ // 以 nums[left] 作为基准数
+ int i = left, j = right;
+ while (i < j)
+ {
+ while (i < j && nums[j] >= nums[left])
+ j--; // 从右向左找首个小于基准数的元素
+ while (i < j && nums[i] <= nums[left])
+ i++; // 从左向右找首个大于基准数的元素
+ swap(nums, i, j); // 交换这两个元素
+ }
+ swap(nums, i, left); // 将基准数交换至两子数组的分界线
+ return i; // 返回基准数的索引
+ }
+
+ /* 快速排序(尾递归优化) */
+ public static void quickSort(int[] nums, int left, int right)
+ {
+ // 子数组长度为 1 时终止
+ while (left < right)
+ {
+ // 哨兵划分操作
+ int pivot = partition(nums, left, right);
+ // 对两个子数组中较短的那个执行快排
+ if (pivot - left < right - pivot)
+ {
+ quickSort(nums, left, pivot - 1); // 递归排序左子数组
+ left = pivot + 1; // 剩余待排序区间为 [pivot + 1, right]
+ }
+ else
+ {
+ quickSort(nums, pivot + 1, right); // 递归排序右子数组
+ right = pivot - 1; // 剩余待排序区间为 [left, pivot - 1]
+ }
+ }
+ }
+ }
+
+ public class quick_sort
+ {
+ [Test]
+ public void Test()
+ {
+ /* 快速排序 */
+ int[] nums = { 2, 4, 1, 0, 3, 5 };
+ QuickSort.quickSort(nums, 0, nums.Length - 1);
+ Console.WriteLine("快速排序完成后 nums = " + string.Join(",", nums));
+
+ /* 快速排序(中位基准数优化) */
+ int[] nums1 = { 2, 4, 1, 0, 3, 5 };
+ QuickSortMedian.quickSort(nums1, 0, nums1.Length - 1);
+ Console.WriteLine("快速排序(中位基准数优化)完成后 nums1 = " + string.Join(",", nums1));
+
+ /* 快速排序(尾递归优化) */
+ int[] nums2 = { 2, 4, 1, 0, 3, 5 };
+ QuickSortTailCall.quickSort(nums2, 0, nums2.Length - 1);
+ Console.WriteLine("快速排序(尾递归优化)完成后 nums2 = " + string.Join(",", nums2));
+ }
+ }
+}
diff --git a/codes/csharp/chapter_stack_and_queue/array_queue.cs b/codes/csharp/chapter_stack_and_queue/array_queue.cs
new file mode 100644
index 000000000..5ad6115ec
--- /dev/null
+++ b/codes/csharp/chapter_stack_and_queue/array_queue.cs
@@ -0,0 +1,120 @@
+/**
+ * File: array_queue.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_stack_and_queue
+{
+
+ /* 基于环形数组实现的队列 */
+ class ArrayQueue {
+ private int[] nums; // 用于存储队列元素的数组
+ private int front = 0; // 头指针,指向队首
+ private int rear = 0; // 尾指针,指向队尾 + 1
+
+ public ArrayQueue(int capacity) {
+ // 初始化数组
+ nums = new int[capacity];
+ }
+
+ /* 获取队列的容量 */
+ public int capacity() {
+ return nums.Length;
+ }
+
+ /* 获取队列的长度 */
+ public int size() {
+ int capacity = this.capacity();
+ // 由于将数组看作为环形,可能 rear < front ,因此需要取余数
+ return (capacity + rear - front) % capacity;
+ }
+
+ /* 判断队列是否为空 */
+ public bool isEmpty() {
+ return rear - front == 0;
+ }
+
+ /* 入队 */
+ public void offer(int num) {
+ if (size() == capacity()) {
+ Console.WriteLine("队列已满");
+ return;
+ }
+ // 尾结点后添加 num
+ nums[rear] = num;
+ // 尾指针向后移动一位,越过尾部后返回到数组头部
+ rear = (rear + 1) % capacity();
+ }
+
+ /* 出队 */
+ public int poll() {
+ int num = peek();
+ // 队头指针向后移动一位,若越过尾部则返回到数组头部
+ front = (front + 1) % capacity();
+ return num;
+ }
+
+ /* 访问队首元素 */
+ public int peek() {
+ if (isEmpty())
+ throw new Exception();
+ return nums[front];
+ }
+
+ /* 返回数组 */
+ public int[] toArray() {
+ int size = this.size();
+ int capacity = this.capacity();
+ // 仅转换有效长度范围内的列表元素
+ int[] res = new int[size];
+ for (int i = 0, j = front; i < size; i++, j++) {
+ res[i] = nums[j % capacity];
+ }
+ return res;
+ }
+ }
+
+ public class array_queue {
+ [Test]
+ public void Test()
+ {
+ /* 初始化队列 */
+ int capacity = 10;
+ ArrayQueue queue = new ArrayQueue(capacity);
+
+ /* 元素入队 */
+ queue.offer(1);
+ queue.offer(3);
+ queue.offer(2);
+ queue.offer(5);
+ queue.offer(4);
+ Console.WriteLine("队列 queue = " + string.Join(",",queue.toArray()));
+
+ /* 访问队首元素 */
+ int peek = queue.peek();
+ Console.WriteLine("队首元素 peek = " + peek);
+
+ /* 元素出队 */
+ int poll = queue.poll();
+ Console.WriteLine("出队元素 poll = " + poll + ",出队后 queue = " + string.Join(",", queue.toArray()));
+
+ /* 获取队列的长度 */
+ int size = queue.size();
+ Console.WriteLine("队列长度 size = " + size);
+
+ /* 判断队列是否为空 */
+ bool isEmpty = queue.isEmpty();
+ Console.WriteLine("队列是否为空 = " + isEmpty);
+
+ /* 测试环形数组 */
+ for (int i = 0; i < 10; i++) {
+ queue.offer(i);
+ queue.poll();
+ Console.WriteLine("第 " + i + " 轮入队 + 出队后 queue = " + string.Join(",", queue.toArray()));
+ }
+ }
+ }
+}
\ No newline at end of file
diff --git a/codes/csharp/chapter_stack_and_queue/array_stack.cs b/codes/csharp/chapter_stack_and_queue/array_stack.cs
new file mode 100644
index 000000000..b7ea6df76
--- /dev/null
+++ b/codes/csharp/chapter_stack_and_queue/array_stack.cs
@@ -0,0 +1,98 @@
+/**
+ * File: array_stack.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_stack_and_queue
+{
+
+ /* 基于数组实现的栈 */
+ class ArrayStack
+ {
+ private List stack;
+ public ArrayStack()
+ {
+ // 初始化列表(动态数组)
+ stack = new();
+ }
+
+ /* 获取栈的长度 */
+ public int size()
+ {
+ return stack.Count();
+ }
+
+ /* 判断栈是否为空 */
+ public bool isEmpty()
+ {
+ return size() == 0;
+ }
+
+ /* 入栈 */
+ public void push(int num)
+ {
+ stack.Add(num);
+ }
+
+ /* 出栈 */
+ public int pop()
+ {
+ if (isEmpty())
+ throw new Exception();
+ var val = peek();
+ stack.RemoveAt(size() - 1);
+ return val;
+ }
+
+ /* 访问栈顶元素 */
+ public int peek()
+ {
+ if (isEmpty())
+ throw new Exception();
+ return stack[size() - 1];
+ }
+
+ /* 将 List 转化为 Array 并返回 */
+ public int[] toArray()
+ {
+ return stack.ToArray();
+ }
+ }
+
+ public class array_stack
+ {
+ [Test]
+ public void Test()
+ {
+ /* 初始化栈 */
+ ArrayStack stack = new ArrayStack();
+
+ /* 元素入栈 */
+ stack.push(1);
+ stack.push(3);
+ stack.push(2);
+ stack.push(5);
+ stack.push(4);
+ Console.WriteLine("栈 stack = " + String.Join(",", stack.toArray()));
+
+ /* 访问栈顶元素 */
+ int peek = stack.peek();
+ Console.WriteLine("栈顶元素 peek = " + peek);
+
+ /* 元素出栈 */
+ int pop = stack.pop();
+ Console.WriteLine("出栈元素 pop = " + pop + ",出栈后 stack = " + String.Join(",", stack.toArray()));
+
+ /* 获取栈的长度 */
+ int size = stack.size();
+ Console.WriteLine("栈的长度 size = " + size);
+
+ /* 判断是否为空 */
+ bool isEmpty = stack.isEmpty();
+ Console.WriteLine("栈是否为空 = " + isEmpty);
+ }
+ }
+}
diff --git a/codes/csharp/chapter_stack_and_queue/linkedlist_queue.cs b/codes/csharp/chapter_stack_and_queue/linkedlist_queue.cs
new file mode 100644
index 000000000..70816c8f0
--- /dev/null
+++ b/codes/csharp/chapter_stack_and_queue/linkedlist_queue.cs
@@ -0,0 +1,124 @@
+/**
+ * File: linkedlist_queue.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_stack_and_queue
+{
+ /* 基于链表实现的队列 */
+ class LinkedListQueue
+ {
+ private ListNode? front, rear; // 头结点 front ,尾结点 rear
+ private int queSize = 0;
+
+ public LinkedListQueue()
+ {
+ front = null;
+ rear = null;
+ }
+
+ /* 获取队列的长度 */
+ public int size()
+ {
+ return queSize;
+ }
+
+ /* 判断队列是否为空 */
+ public bool isEmpty()
+ {
+ return size() == 0;
+ }
+
+ /* 入队 */
+ public void offer(int num)
+ {
+ // 尾结点后添加 num
+ ListNode node = new ListNode(num);
+ // 如果队列为空,则令头、尾结点都指向该结点
+ if (front == null)
+ {
+ front = node;
+ rear = node;
+ // 如果队列不为空,则将该结点添加到尾结点后
+ }
+ else if (rear != null)
+ {
+ rear.next = node;
+ rear = node;
+ }
+ queSize++;
+ }
+
+ /* 出队 */
+ public int poll()
+ {
+ int num = peek();
+ // 删除头结点
+ front = front?.next;
+ queSize--;
+ return num;
+ }
+
+ /* 访问队首元素 */
+ public int peek()
+ {
+ if (size() == 0 || front == null)
+ throw new Exception();
+ return front.val;
+ }
+
+ /* 将链表转化为 Array 并返回 */
+ public int[] toArray()
+ {
+ if (front == null)
+ return Array.Empty();
+
+ ListNode node = front;
+ int[] res = new int[size()];
+ for (int i = 0; i < res.Length; i++)
+ {
+ res[i] = node.val;
+ node = node.next;
+ }
+ return res;
+ }
+ }
+
+ public class linkedlist_queue
+ {
+ [Test]
+ public void Test()
+ {
+ /* 初始化队列 */
+ LinkedListQueue queue = new LinkedListQueue();
+
+ /* 元素入队 */
+ queue.offer(1);
+ queue.offer(3);
+ queue.offer(2);
+ queue.offer(5);
+ queue.offer(4);
+ Console.WriteLine("队列 queue = " + String.Join(",", queue.toArray()));
+
+ /* 访问队首元素 */
+ int peek = queue.peek();
+ Console.WriteLine("队首元素 peek = " + peek);
+
+ /* 元素出队 */
+ int poll = queue.poll();
+ Console.WriteLine("出队元素 poll = " + poll + ",出队后 queue = " + String.Join(",", queue.toArray()));
+
+ /* 获取队列的长度 */
+ int size = queue.size();
+ Console.WriteLine("队列长度 size = " + size);
+
+ /* 判断队列是否为空 */
+ bool isEmpty = queue.isEmpty();
+ Console.WriteLine("队列是否为空 = " + isEmpty);
+ }
+ }
+}
\ No newline at end of file
diff --git a/codes/csharp/chapter_stack_and_queue/linkedlist_stack.cs b/codes/csharp/chapter_stack_and_queue/linkedlist_stack.cs
new file mode 100644
index 000000000..78a409449
--- /dev/null
+++ b/codes/csharp/chapter_stack_and_queue/linkedlist_stack.cs
@@ -0,0 +1,113 @@
+/**
+ * File: linkedlist_stack.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_stack_and_queue
+{
+ class LinkedListStack
+ {
+ private ListNode? stackPeek; // 将头结点作为栈顶
+ private int stkSize = 0; // 栈的长度
+
+ public LinkedListStack()
+ {
+ stackPeek = null;
+ }
+
+ /* 获取栈的长度 */
+ public int size()
+ {
+ return stkSize;
+ }
+
+ /* 判断栈是否为空 */
+ public bool isEmpty()
+ {
+ return size() == 0;
+ }
+
+ /* 入栈 */
+ public void push(int num)
+ {
+ ListNode node = new ListNode(num);
+ node.next = stackPeek;
+ stackPeek = node;
+ stkSize++;
+ }
+
+ /* 出栈 */
+ public int pop()
+ {
+ if (stackPeek == null)
+ throw new Exception();
+
+ int num = peek();
+ stackPeek = stackPeek.next;
+ stkSize--;
+ return num;
+ }
+
+ /* 访问栈顶元素 */
+ public int peek()
+ {
+ if (size() == 0 || stackPeek==null)
+ throw new Exception();
+ return stackPeek.val;
+ }
+
+ /* 将 List 转化为 Array 并返回 */
+ public int[] toArray()
+ {
+ if (stackPeek == null)
+ return Array.Empty();
+
+ ListNode node = stackPeek;
+ int[] res = new int[size()];
+ for (int i = res.Length - 1; i >= 0; i--)
+ {
+ res[i] = node.val;
+ node = node.next;
+ }
+ return res;
+ }
+ }
+
+ public class linkedlist_stack
+ {
+ [Test]
+ public void Test()
+ {
+ /* 初始化栈 */
+ LinkedListStack stack = new LinkedListStack();
+
+ /* 元素入栈 */
+ stack.push(1);
+ stack.push(3);
+ stack.push(2);
+ stack.push(5);
+ stack.push(4);
+ Console.WriteLine("栈 stack = " + String.Join(",",stack.toArray()));
+
+ /* 访问栈顶元素 */
+ int peek = stack.peek();
+ Console.WriteLine("栈顶元素 peek = " + peek);
+
+ /* 元素出栈 */
+ int pop = stack.pop();
+ Console.WriteLine("出栈元素 pop = " + pop + ",出栈后 stack = " + String.Join(",",stack.toArray()));
+
+ /* 获取栈的长度 */
+ int size = stack.size();
+ Console.WriteLine("栈的长度 size = " + size);
+
+ /* 判断是否为空 */
+ bool isEmpty = stack.isEmpty();
+ Console.WriteLine("栈是否为空 = " + isEmpty);
+ }
+ }
+}
\ No newline at end of file
diff --git a/codes/csharp/chapter_stack_and_queue/queue.cs b/codes/csharp/chapter_stack_and_queue/queue.cs
new file mode 100644
index 000000000..a5ce96953
--- /dev/null
+++ b/codes/csharp/chapter_stack_and_queue/queue.cs
@@ -0,0 +1,45 @@
+/**
+ * File: queue.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_stack_and_queue
+{
+ public class queue
+ {
+ [Test]
+ public void Test()
+ {
+ /* 初始化队列 */
+ Queue queue = new();
+
+ /* 元素入队 */
+ queue.Enqueue(1);
+ queue.Enqueue(3);
+ queue.Enqueue(2);
+ queue.Enqueue(5);
+ queue.Enqueue(4);
+ Console.WriteLine("队列 queue = " + String.Join(",", queue.ToArray()));
+
+ /* 访问队首元素 */
+ int peek = queue.Peek();
+ Console.WriteLine("队首元素 peek = " + peek);
+
+ /* 元素出队 */
+ int poll = queue.Dequeue();
+ Console.WriteLine("出队元素 poll = " + poll + ",出队后 queue = " + String.Join(",", queue.ToArray()));
+
+ /* 获取队列的长度 */
+ int size = queue.Count();
+ Console.WriteLine("队列长度 size = " + size);
+
+ /* 判断队列是否为空 */
+ bool isEmpty = queue.Count() == 0;
+ Console.WriteLine("队列是否为空 = " + isEmpty);
+ }
+ }
+
+}
diff --git a/codes/csharp/chapter_stack_and_queue/stack.cs b/codes/csharp/chapter_stack_and_queue/stack.cs
new file mode 100644
index 000000000..c19666b72
--- /dev/null
+++ b/codes/csharp/chapter_stack_and_queue/stack.cs
@@ -0,0 +1,45 @@
+/**
+ * File: stack.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using NUnit.Framework;
+
+namespace hello_algo.chapter_stack_and_queue
+{
+ public class stack
+ {
+ [Test]
+ public void Test()
+ {
+ /* 初始化栈 */
+ Stack stack = new();
+
+ /* 元素入栈 */
+ stack.Push(1);
+ stack.Push(3);
+ stack.Push(2);
+ stack.Push(5);
+ stack.Push(4);
+ // 请注意,stack.ToArray() 得到的是倒序序列,即索引 0 为栈顶
+ Console.WriteLine("栈 stack = " + string.Join(",", stack.ToArray()));
+
+ /* 访问栈顶元素 */
+ int peek = stack.Peek();
+ Console.WriteLine("栈顶元素 peek = " + peek);
+
+ /* 元素出栈 */
+ int pop = stack.Pop();
+ Console.WriteLine("出栈元素 pop = " + pop + ",出栈后 stack = " + string.Join(",", stack.ToArray()));
+
+ /* 获取栈的长度 */
+ int size = stack.Count();
+ Console.WriteLine("栈的长度 size = " + size);
+
+ /* 判断是否为空 */
+ bool isEmpty = stack.Count() == 0;
+ Console.WriteLine("栈是否为空 = " + isEmpty);
+ }
+ }
+}
\ No newline at end of file
diff --git a/codes/csharp/chapter_tree/avl_tree.cs b/codes/csharp/chapter_tree/avl_tree.cs
new file mode 100644
index 000000000..f2dcde219
--- /dev/null
+++ b/codes/csharp/chapter_tree/avl_tree.cs
@@ -0,0 +1,269 @@
+/**
+ * File: avl_tree.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_tree
+{
+ // Tree class
+ class AVLTree
+ {
+ public TreeNode? root; // 根节点
+
+ /* 获取结点高度 */
+ public int height(TreeNode? node)
+ {
+ // 空结点高度为 -1 ,叶结点高度为 0
+ return node == null ? -1 : node.height;
+ }
+
+ /* 更新结点高度 */
+ private void updateHeight(TreeNode node)
+ {
+ // 结点高度等于最高子树高度 + 1
+ node.height = Math.Max(height(node.left), height(node.right)) + 1;
+ }
+
+ /* 获取平衡因子 */
+ public int balanceFactor(TreeNode? node)
+ {
+ // 空结点平衡因子为 0
+ if (node == null) return 0;
+ // 结点平衡因子 = 左子树高度 - 右子树高度
+ return height(node.left) - height(node.right);
+ }
+
+ /* 右旋操作 */
+ TreeNode? rightRotate(TreeNode? node)
+ {
+ if (node == null)
+ return null;
+
+ TreeNode? child = node.left;
+ TreeNode? grandChild = child?.right;
+ // 以 child 为原点,将 node 向右旋转
+ child.right = node;
+ node.left = grandChild;
+ // 更新结点高度
+ updateHeight(node);
+ updateHeight(child);
+ // 返回旋转后子树的根节点
+ return child;
+ }
+
+ /* 左旋操作 */
+ TreeNode? leftRotate(TreeNode? node)
+ {
+ if (node == null)
+ return null;
+
+ TreeNode? child = node.right;
+ TreeNode? grandChild = child?.left;
+ // 以 child 为原点,将 node 向左旋转
+ child.left = node;
+ node.right = grandChild;
+ // 更新结点高度
+ updateHeight(node);
+ updateHeight(child);
+ // 返回旋转后子树的根节点
+ return child;
+ }
+
+ /* 执行旋转操作,使该子树重新恢复平衡 */
+ TreeNode? rotate(TreeNode? node)
+ {
+ if (node == null)
+ return node;
+
+ // 获取结点 node 的平衡因子
+ int balanceFactorInt = balanceFactor(node);
+ // 左偏树
+ if (balanceFactorInt > 1)
+ {
+ if (balanceFactor(node.left) >= 0)
+ {
+ // 右旋
+ return rightRotate(node);
+ }
+ else
+ {
+ // 先左旋后右旋
+ node.left = leftRotate(node?.left);
+ return rightRotate(node);
+ }
+ }
+ // 右偏树
+ if (balanceFactorInt < -1)
+ {
+ if (balanceFactor(node.right) <= 0)
+ {
+ // 左旋
+ return leftRotate(node);
+ }
+ else
+ {
+ // 先右旋后左旋
+ node.right = rightRotate(node?.right);
+ return leftRotate(node);
+ }
+ }
+ // 平衡树,无需旋转,直接返回
+ return node;
+ }
+
+ /* 插入结点 */
+ public TreeNode? insert(int val)
+ {
+ root = insertHelper(root, val);
+ return root;
+ }
+
+ /* 递归插入结点(辅助函数) */
+ private TreeNode? insertHelper(TreeNode? node, int val)
+ {
+ if (node == null) return new TreeNode(val);
+ /* 1. 查找插入位置,并插入结点 */
+ if (val < node.val)
+ node.left = insertHelper(node.left, val);
+ else if (val > node.val)
+ node.right = insertHelper(node.right, val);
+ else
+ return node; // 重复结点不插入,直接返回
+ updateHeight(node); // 更新结点高度
+ /* 2. 执行旋转操作,使该子树重新恢复平衡 */
+ node = rotate(node);
+ // 返回子树的根节点
+ return node;
+ }
+
+ /* 删除结点 */
+ public TreeNode? remove(int val)
+ {
+ root = removeHelper(root, val);
+ return root;
+ }
+
+ /* 递归删除结点(辅助函数) */
+ private TreeNode? removeHelper(TreeNode? node, int val)
+ {
+ if (node == null) return null;
+ /* 1. 查找结点,并删除之 */
+ if (val < node.val)
+ node.left = removeHelper(node.left, val);
+ else if (val > node.val)
+ node.right = removeHelper(node.right, val);
+ else
+ {
+ if (node.left == null || node.right == null)
+ {
+ TreeNode? child = node.left != null ? node.left : node.right;
+ // 子结点数量 = 0 ,直接删除 node 并返回
+ if (child == null)
+ return null;
+ // 子结点数量 = 1 ,直接删除 node
+ else
+ node = child;
+ }
+ else
+ {
+ // 子结点数量 = 2 ,则将中序遍历的下个结点删除,并用该结点替换当前结点
+ TreeNode? temp = minNode(node.right);
+ node.right = removeHelper(node.right, temp.val);
+ node.val = temp.val;
+ }
+ }
+ updateHeight(node); // 更新结点高度
+ /* 2. 执行旋转操作,使该子树重新恢复平衡 */
+ node = rotate(node);
+ // 返回子树的根节点
+ return node;
+ }
+
+ /* 获取最小结点 */
+ private TreeNode? minNode(TreeNode? node)
+ {
+ if (node == null) return node;
+ // 循环访问左子结点,直到叶结点时为最小结点,跳出
+ while (node.left != null)
+ {
+ node = node.left;
+ }
+ return node;
+ }
+
+ /* 查找结点 */
+ public TreeNode? search(int val)
+ {
+ TreeNode? cur = root;
+ // 循环查找,越过叶结点后跳出
+ while (cur != null)
+ {
+ // 目标结点在 root 的右子树中
+ if (cur.val < val)
+ cur = cur.right;
+ // 目标结点在 root 的左子树中
+ else if (cur.val > val)
+ cur = cur.left;
+ // 找到目标结点,跳出循环
+ else
+ break;
+ }
+ // 返回目标结点
+ return cur;
+ }
+ }
+
+ public class avl_tree
+ {
+ static void testInsert(AVLTree tree, int val)
+ {
+ tree.insert(val);
+ Console.WriteLine("\n插入结点 " + val + " 后,AVL 树为");
+ PrintUtil.PrintTree(tree.root);
+ }
+
+ static void testRemove(AVLTree tree, int val)
+ {
+ tree.remove(val);
+ Console.WriteLine("\n删除结点 " + val + " 后,AVL 树为");
+ PrintUtil.PrintTree(tree.root);
+ }
+
+ [Test]
+ public void Test()
+ {
+ /* 初始化空 AVL 树 */
+ AVLTree avlTree = new AVLTree();
+
+ /* 插入结点 */
+ // 请关注插入结点后,AVL 树是如何保持平衡的
+ testInsert(avlTree, 1);
+ testInsert(avlTree, 2);
+ testInsert(avlTree, 3);
+ testInsert(avlTree, 4);
+ testInsert(avlTree, 5);
+ testInsert(avlTree, 8);
+ testInsert(avlTree, 7);
+ testInsert(avlTree, 9);
+ testInsert(avlTree, 10);
+ testInsert(avlTree, 6);
+
+ /* 插入重复结点 */
+ testInsert(avlTree, 7);
+
+ /* 删除结点 */
+ // 请关注删除结点后,AVL 树是如何保持平衡的
+ testRemove(avlTree, 8); // 删除度为 0 的结点
+ testRemove(avlTree, 5); // 删除度为 1 的结点
+ testRemove(avlTree, 4); // 删除度为 2 的结点
+
+ /* 查询结点 */
+ TreeNode? node = avlTree.search(7);
+ Console.WriteLine("\n查找到的结点对象为 " + node + ",结点值 = " + node?.val);
+ }
+ }
+}
diff --git a/codes/csharp/chapter_tree/binary_search_tree.cs b/codes/csharp/chapter_tree/binary_search_tree.cs
new file mode 100644
index 000000000..8224317df
--- /dev/null
+++ b/codes/csharp/chapter_tree/binary_search_tree.cs
@@ -0,0 +1,186 @@
+/**
+ * File: binary_search_tree.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_tree
+{
+ class BinarySearchTree
+ {
+ TreeNode? root;
+
+ public BinarySearchTree(int[] nums) {
+ Array.Sort(nums); // 排序数组
+ root = buildTree(nums, 0, nums.Length - 1); // 构建二叉搜索树
+ }
+
+ /* 获取二叉树根结点 */
+ public TreeNode? getRoot() {
+ return root;
+ }
+
+ /* 构建二叉搜索树 */
+ public TreeNode? buildTree(int[] nums, int i, int j) {
+ if (i > j) return null;
+ // 将数组中间结点作为根结点
+ int mid = (i + j) / 2;
+ TreeNode root = new TreeNode(nums[mid]);
+ // 递归建立左子树和右子树
+ root.left = buildTree(nums, i, mid - 1);
+ root.right = buildTree(nums, mid + 1, j);
+ return root;
+ }
+
+ ///
+ /// 查找结点
+ ///
+ ///
+ ///
+ public TreeNode? search(int num)
+ {
+ TreeNode? cur = root;
+ // 循环查找,越过叶结点后跳出
+ while (cur != null)
+ {
+ // 目标结点在 root 的右子树中
+ if (cur.val < num) cur = cur.right;
+ // 目标结点在 root 的左子树中
+ else if (cur.val > num) cur = cur.left;
+ // 找到目标结点,跳出循环
+ else break;
+ }
+ // 返回目标结点
+ return cur;
+ }
+
+ /* 插入结点 */
+ public TreeNode? insert(int num)
+ {
+ // 若树为空,直接提前返回
+ if (root == null) return null;
+ TreeNode? cur = root, pre = null;
+ // 循环查找,越过叶结点后跳出
+ while (cur != null)
+ {
+ // 找到重复结点,直接返回
+ if (cur.val == num) return null;
+ pre = cur;
+ // 插入位置在 root 的右子树中
+ if (cur.val < num) cur = cur.right;
+ // 插入位置在 root 的左子树中
+ else cur = cur.left;
+ }
+
+ // 插入结点 val
+ TreeNode node = new TreeNode(num);
+ if (pre != null)
+ {
+ if (pre.val < num) pre.right = node;
+ else pre.left = node;
+ }
+ return node;
+ }
+
+
+ /* 删除结点 */
+ public TreeNode? remove(int num)
+ {
+ // 若树为空,直接提前返回
+ if (root == null) return null;
+ TreeNode? cur = root, pre = null;
+ // 循环查找,越过叶结点后跳出
+ while (cur != null)
+ {
+ // 找到待删除结点,跳出循环
+ if (cur.val == num) break;
+ pre = cur;
+ // 待删除结点在 root 的右子树中
+ if (cur.val < num) cur = cur.right;
+ // 待删除结点在 root 的左子树中
+ else cur = cur.left;
+ }
+ // 若无待删除结点,则直接返回
+ if (cur == null || pre == null) return null;
+ // 子结点数量 = 0 or 1
+ if (cur.left == null || cur.right == null)
+ {
+ // 当子结点数量 = 0 / 1 时, child = null / 该子结点
+ TreeNode? child = cur.left != null ? cur.left : cur.right;
+ // 删除结点 cur
+ if (pre.left == cur)
+ {
+ pre.left = child;
+ }
+ else
+ {
+ pre.right = child;
+ }
+
+ }
+ // 子结点数量 = 2
+ else
+ {
+ // 获取中序遍历中 cur 的下一个结点
+ TreeNode? nex = min(cur.right);
+ if (nex != null)
+ {
+ int tmp = nex.val;
+ // 递归删除结点 nex
+ remove(nex.val);
+ // 将 nex 的值复制给 cur
+ cur.val = tmp;
+ }
+ }
+ return cur;
+ }
+
+ /* 获取最小结点 */
+ private TreeNode? min(TreeNode? root)
+ {
+ if (root == null) return root;
+ // 循环访问左子结点,直到叶结点时为最小结点,跳出
+ while (root.left != null)
+ {
+ root = root.left;
+ }
+ return root;
+ }
+ }
+
+ public class binary_search_tree
+ {
+ [Test]
+ public void Test()
+ {
+ /* 初始化二叉搜索树 */
+ int[] nums = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 };
+ BinarySearchTree bst = new BinarySearchTree(nums);
+ Console.WriteLine("\n初始化的二叉树为\n");
+ PrintUtil.PrintTree(bst.getRoot());
+
+ /* 查找结点 */
+ TreeNode? node = bst.search(5);
+ Console.WriteLine("\n查找到的结点对象为 " + node + ",结点值 = " + node.val);
+
+ /* 插入结点 */
+ node = bst.insert(16);
+ Console.WriteLine("\n插入结点 16 后,二叉树为\n");
+ PrintUtil.PrintTree(bst.getRoot());
+
+ /* 删除结点 */
+ bst.remove(1);
+ Console.WriteLine("\n删除结点 1 后,二叉树为\n");
+ PrintUtil.PrintTree(bst.getRoot());
+ bst.remove(2);
+ Console.WriteLine("\n删除结点 2 后,二叉树为\n");
+ PrintUtil.PrintTree(bst.getRoot());
+ bst.remove(4);
+ Console.WriteLine("\n删除结点 4 后,二叉树为\n");
+ PrintUtil.PrintTree(bst.getRoot());
+ }
+ }
+}
diff --git a/codes/csharp/chapter_tree/binary_tree.cs b/codes/csharp/chapter_tree/binary_tree.cs
new file mode 100644
index 000000000..275a69f93
--- /dev/null
+++ b/codes/csharp/chapter_tree/binary_tree.cs
@@ -0,0 +1,46 @@
+/**
+ * File: binary_tree.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_tree
+{
+
+ public class binary_tree
+ {
+ [Test]
+ public void Test()
+ {
+ /* 初始化二叉树 */
+ // 初始化结点
+ TreeNode n1 = new TreeNode(1);
+ TreeNode n2 = new TreeNode(2);
+ TreeNode n3 = new TreeNode(3);
+ TreeNode n4 = new TreeNode(4);
+ TreeNode n5 = new TreeNode(5);
+ // 构建引用指向(即指针)
+ n1.left = n2;
+ n1.right = n3;
+ n2.left = n4;
+ n2.right = n5;
+ Console.WriteLine("\n初始化二叉树\n");
+ PrintUtil.PrintTree(n1);
+
+ /* 插入与删除结点 */
+ TreeNode P = new TreeNode(0);
+ // 在 n1 -> n2 中间插入结点 P
+ n1.left = P;
+ P.left = n2;
+ Console.WriteLine("\n插入结点 P 后\n");
+ PrintUtil.PrintTree(n1);
+ // 删除结点 P
+ n1.left = n2;
+ Console.WriteLine("\n删除结点 P 后\n");
+ PrintUtil.PrintTree(n1);
+ }
+ }
+}
\ No newline at end of file
diff --git a/codes/csharp/chapter_tree/binary_tree_bfs.cs b/codes/csharp/chapter_tree/binary_tree_bfs.cs
new file mode 100644
index 000000000..31f707246
--- /dev/null
+++ b/codes/csharp/chapter_tree/binary_tree_bfs.cs
@@ -0,0 +1,53 @@
+/**
+ * File: binary_tree_bfs.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_tree
+{
+ public class binary_tree_bfs
+ {
+
+ ///
+ /// 层序遍历
+ ///
+ ///
+ ///
+ public List hierOrder(TreeNode root)
+ {
+ // 初始化队列,加入根结点
+ Queue queue = new();
+ queue.Enqueue(root);
+ // 初始化一个列表,用于保存遍历序列
+ List list = new();
+ while (queue.Count != 0)
+ {
+ TreeNode node = queue.Dequeue(); // 队列出队
+ list.Add(node.val); // 保存结点值
+ if (node.left != null)
+ queue.Enqueue(node.left); // 左子结点入队
+ if (node.right != null)
+ queue.Enqueue(node.right); // 右子结点入队
+ }
+ return list;
+ }
+
+ [Test]
+ public void Test()
+ {
+ /* 初始化二叉树 */
+ // 这里借助了一个从数组直接生成二叉树的函数
+ TreeNode? root = TreeNode.ArrToTree(new int?[] {
+ 1, 2, 3, 4, 5, 6, 7, null, null, null, null, null, null, null, null});
+ Console.WriteLine("\n初始化二叉树\n");
+ PrintUtil.PrintTree(root);
+
+ List list = hierOrder(root);
+ Console.WriteLine("\n层序遍历的结点打印序列 = " + string.Join(",", list.ToArray()));
+ }
+ }
+}
diff --git a/codes/csharp/chapter_tree/binary_tree_dfs.cs b/codes/csharp/chapter_tree/binary_tree_dfs.cs
new file mode 100644
index 000000000..6e38ebe4c
--- /dev/null
+++ b/codes/csharp/chapter_tree/binary_tree_dfs.cs
@@ -0,0 +1,78 @@
+/**
+ * File: binary_tree_bfs.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+using hello_algo.include;
+using NUnit.Framework;
+
+namespace hello_algo.chapter_tree
+{
+ public class binary_tree_dfs
+ {
+ List list = new();
+
+ ///
+ /// 前序遍历
+ ///
+ ///
+ void preOrder(TreeNode? root)
+ {
+ if (root == null) return;
+ // 访问优先级:根结点 -> 左子树 -> 右子树
+ list.Add(root.val);
+ preOrder(root.left);
+ preOrder(root.right);
+ }
+
+ ///
+ /// 中序遍历
+ ///
+ ///
+ void inOrder(TreeNode? root)
+ {
+ if (root == null) return;
+ // 访问优先级:左子树 -> 根结点 -> 右子树
+ inOrder(root.left);
+ list.Add(root.val);
+ inOrder(root.right);
+ }
+
+ ///
+ /// 后序遍历
+ ///
+ ///
+ void postOrder(TreeNode? root)
+ {
+ if (root == null) return;
+ // 访问优先级:左子树 -> 右子树 -> 根结点
+ postOrder(root.left);
+ postOrder(root.right);
+ list.Add(root.val);
+ }
+
+ [Test]
+ public void Test()
+ {
+ /* 初始化二叉树 */
+ // 这里借助了一个从数组直接生成二叉树的函数
+ TreeNode? root = TreeNode.ArrToTree(new int?[] {
+ 1, 2, 3, 4, 5, 6, 7, null, null, null, null, null, null, null, null});
+ Console.WriteLine("\n初始化二叉树\n");
+ PrintUtil.PrintTree(root);
+
+ list.Clear();
+ preOrder(root);
+ Console.WriteLine("\n前序遍历的结点打印序列 = " + string.Join(",", list.ToArray()));
+
+ list.Clear();
+ inOrder(root);
+ Console.WriteLine("\n中序遍历的结点打印序列 = " + string.Join(",", list.ToArray()));
+
+ list.Clear();
+ postOrder(root);
+ Console.WriteLine("\n后序遍历的结点打印序列 = " + string.Join(",", list.ToArray()));
+ }
+ }
+}
diff --git a/codes/csharp/include/ListNode.cs b/codes/csharp/include/ListNode.cs
index 580a1d376..0fe2913eb 100644
--- a/codes/csharp/include/ListNode.cs
+++ b/codes/csharp/include/ListNode.cs
@@ -10,7 +10,7 @@ namespace hello_algo.include
public class ListNode
{
public int val;
- public ListNode next;
+ public ListNode? next;
///
/// Generate a linked list with an array
@@ -26,7 +26,7 @@ namespace hello_algo.include
///
///
///
- public static ListNode ArrToLinkedList(int[] arr)
+ public static ListNode? ArrToLinkedList(int[] arr)
{
ListNode dum = new ListNode(0);
ListNode head = dum;
@@ -44,7 +44,7 @@ namespace hello_algo.include
///
///
///
- public static ListNode GetListNode(ListNode head, int val)
+ public static ListNode? GetListNode(ListNode? head, int val)
{
while (head != null && head.val != val)
{
diff --git a/codes/csharp/include/PrintUtil.cs b/codes/csharp/include/PrintUtil.cs
new file mode 100644
index 000000000..06e85a93c
--- /dev/null
+++ b/codes/csharp/include/PrintUtil.cs
@@ -0,0 +1,124 @@
+/**
+ * File: PrintUtil.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+namespace hello_algo.include
+{
+ public class Trunk
+ {
+ public Trunk? prev;
+ public String str;
+
+ public Trunk(Trunk? prev, String str)
+ {
+ this.prev = prev;
+ this.str = str;
+ }
+ };
+
+ public class PrintUtil
+ {
+ /**
+ * Print a linked list
+ * @param head
+ */
+ public static void PrintLinkedList(ListNode head)
+ {
+ List list = new();
+ while (head != null)
+ {
+ list.Add(head.val.ToString());
+ head = head.next;
+ }
+ Console.Write(String.Join(" -> ", list));
+ }
+
+ /**
+ * The interface of the tree printer
+ * This tree printer is borrowed from TECHIE DELIGHT
+ * https://www.techiedelight.com/c-program-print-binary-tree/
+ * @param root
+ */
+ public static void PrintTree(TreeNode? root)
+ {
+ PrintTree(root, null, false);
+ }
+
+ /**
+ * Print a binary tree
+ * @param root
+ * @param prev
+ * @param isLeft
+ */
+ public static void PrintTree(TreeNode? root, Trunk? prev, bool isLeft)
+ {
+ if (root == null)
+ {
+ return;
+ }
+
+ String prev_str = " ";
+ Trunk trunk = new Trunk(prev, prev_str);
+
+ PrintTree(root.right, trunk, true);
+
+ if (prev == null)
+ {
+ trunk.str = "———";
+ }
+ else if (isLeft)
+ {
+ trunk.str = "/———";
+ prev_str = " |";
+ }
+ else
+ {
+ trunk.str = "\\———";
+ prev.str = prev_str;
+ }
+
+ showTrunks(trunk);
+ Console.WriteLine(" " + root.val);
+
+ if (prev != null)
+ {
+ prev.str = prev_str;
+ }
+ trunk.str = " |";
+
+ PrintTree(root.left, trunk, false);
+ }
+
+ /**
+ * Helper function to print branches of the binary tree
+ * @param p
+ */
+ public static void showTrunks(Trunk? p)
+ {
+ if (p == null)
+ {
+ return;
+ }
+
+ showTrunks(p.prev);
+ Console.Write(p.str);
+ }
+
+ /**
+ * Print a hash map
+ * @param
+ * @param
+ * @param map
+ */
+ public static void printHashMap(Dictionary map) where K : notnull
+ {
+ foreach (var kv in map.Keys)
+ {
+ Console.WriteLine(kv.ToString() + " -> " + map[kv]?.ToString());
+ }
+ }
+ }
+
+}
diff --git a/codes/csharp/include/TreeNode.cs b/codes/csharp/include/TreeNode.cs
new file mode 100644
index 000000000..e5cacd59e
--- /dev/null
+++ b/codes/csharp/include/TreeNode.cs
@@ -0,0 +1,98 @@
+/**
+ * File: TreeNode.cs
+ * Created Time: 2022-12-23
+ * Author: haptear (haptear@hotmail.com)
+ */
+
+namespace hello_algo.include
+{
+ public class TreeNode
+ {
+ public int val; // 结点值
+ public int height; // 结点高度
+ public TreeNode? left; // 左子结点引用
+ public TreeNode? right; // 右子结点引用
+
+ public TreeNode(int x)
+ {
+ val = x;
+ }
+
+ /**
+ * Generate a binary tree with an array
+ * @param arr
+ * @return
+ */
+ public static TreeNode? ArrToTree(int?[] arr)
+ {
+ if (arr.Length == 0 || arr[0] == null)
+ return null;
+
+ TreeNode root = new TreeNode((int) arr[0]);
+ Queue queue = new Queue();
+ queue.Enqueue(root);
+ int i = 1;
+ while (queue.Count!=0)
+ {
+ TreeNode node = queue.Dequeue();
+ if (arr[i] != null)
+ {
+ node.left = new TreeNode((int) arr[i]);
+ queue.Enqueue(node.left);
+ }
+ i++;
+ if (arr[i] != null)
+ {
+ node.right = new TreeNode((int) arr[i]);
+ queue.Enqueue(node.right);
+ }
+ i++;
+ }
+ return root;
+ }
+
+ /**
+ * Serialize a binary tree to a list
+ * @param root
+ * @return
+ */
+ public static List TreeToList(TreeNode root)
+ {
+ List list = new();
+ if (root == null) return list;
+ Queue queue = new();
+ while (queue.Count != 0)
+ {
+ TreeNode? node = queue.Dequeue();
+ if (node != null)
+ {
+ list.Add(node.val);
+ queue.Enqueue(node.left);
+ queue.Enqueue(node.right);
+ }
+ else
+ {
+ list.Add(null);
+ }
+ }
+ return list;
+ }
+
+ /**
+ * Get a tree node with specific value in a binary tree
+ * @param root
+ * @param val
+ * @return
+ */
+ public static TreeNode? GetTreeNode(TreeNode? root, int val)
+ {
+ if (root == null)
+ return null;
+ if (root.val == val)
+ return root;
+ TreeNode? left = GetTreeNode(root.left, val);
+ TreeNode? right = GetTreeNode(root.right, val);
+ return left != null ? left : right;
+ }
+ }
+}
diff --git a/docs/chapter_array_and_linkedlist/array.md b/docs/chapter_array_and_linkedlist/array.md
index 2ad57f0f3..3228e678f 100644
--- a/docs/chapter_array_and_linkedlist/array.md
+++ b/docs/chapter_array_and_linkedlist/array.md
@@ -74,9 +74,6 @@ comments: true
/* 初始化数组 */
int[] arr = new int[5]; // { 0, 0, 0, 0, 0 }
int[] nums = { 1, 3, 2, 5, 4 };
-
- var arr2=new int[5]; // { 0, 0, 0, 0, 0 }
- var nums2=new int[]{1,2,3,4,5};
```
## 数组优点
diff --git a/docs/chapter_array_and_linkedlist/linked_list.md b/docs/chapter_array_and_linkedlist/linked_list.md
index 412d09e79..afff4b13f 100644
--- a/docs/chapter_array_and_linkedlist/linked_list.md
+++ b/docs/chapter_array_and_linkedlist/linked_list.md
@@ -208,13 +208,13 @@ comments: true
=== "C#"
```csharp title=""
- // 初始化链表 1 -> 3 -> 2 -> 5 -> 4
- // 初始化各结点
- n0 = new ListNode(1);
- n1 = new ListNode(3);
- n2 = new ListNode(2);
- n3 = new ListNode(5);
- n4 = new ListNode(4);
+ /* 初始化链表 1 -> 3 -> 2 -> 5 -> 4 */
+ // 初始化各个结点
+ ListNode n0 = new ListNode(1);
+ ListNode n1 = new ListNode(3);
+ ListNode n2 = new ListNode(2);
+ ListNode n3 = new ListNode(5);
+ ListNode n4 = new ListNode(4);
// 构建引用指向
n0.next = n1;
n1.next = n2;
diff --git a/docs/chapter_array_and_linkedlist/list.md b/docs/chapter_array_and_linkedlist/list.md
index 2098a82c1..0868b3eee 100644
--- a/docs/chapter_array_and_linkedlist/list.md
+++ b/docs/chapter_array_and_linkedlist/list.md
@@ -83,7 +83,12 @@ comments: true
=== "C#"
```csharp title="list.cs"
-
+ /* 初始化列表 */
+ // 无初始值
+ List list1 = new ();
+ // 有初始值(注意数组的元素类型需为 int[] 的包装类 Integer[])
+ int[] numbers = new int[] { 1, 3, 2, 5, 4 };
+ List list = numbers.ToList();
```
**访问与更新元素。** 列表的底层数据结构是数组,因此可以在 $O(1)$ 时间内访问与更新元素,效率很高。
@@ -157,7 +162,11 @@ comments: true
=== "C#"
```csharp title="list.cs"
+ /* 访问元素 */
+ int num = list[1];
+ /* 更新元素 */
+ list[1]=0;
```
**在列表中添加、插入、删除元素。** 相对于数组,列表可以自由地添加与删除元素。在列表尾部添加元素的时间复杂度为 $O(1)$ ,但是插入与删除元素的效率仍与数组一样低,时间复杂度为 $O(N)$ 。
@@ -291,7 +300,21 @@ comments: true
=== "C#"
```csharp title="list.cs"
+ /* 清空列表 */
+ list.Clear();
+ /* 尾部添加元素 */
+ list.Add(1);
+ list.Add(3);
+ list.Add(2);
+ list.Add(5);
+ list.Add(4);
+
+ /* 中间插入元素 */
+ list.Insert(3, 6);
+
+ /* 删除元素 */
+ list.RemoveAt(3);
```
**遍历列表。** 与数组一样,列表可以使用索引遍历,也可以使用 `for-each` 直接遍历。
@@ -353,9 +376,9 @@ comments: true
/* 直接遍历列表元素 */
count = 0
- for range list {
- count++
- }
+ for range list {
+ count++
+ }
```
=== "JavaScript"
@@ -399,7 +422,19 @@ comments: true
=== "C#"
```csharp title="list.cs"
+ /* 通过索引遍历列表 */
+ int count = 0;
+ for (int i = 0; i < list.Count(); i++)
+ {
+ count++;
+ }
+ /* 直接遍历列表元素 */
+ count = 0;
+ foreach (int n in list)
+ {
+ count++;
+ }
```
**拼接两个列表。** 再创建一个新列表 `list1` ,我们可以将其中一个列表拼接到另一个的尾部。
@@ -462,7 +497,9 @@ comments: true
=== "C#"
```csharp title="list.cs"
-
+ /* 拼接两个列表 */
+ List list1 = new() { 6, 8, 7, 10, 9 };
+ list.AddRange(list1);
```
**排序列表。** 排序也是常用的方法之一,完成列表排序后,我们就可以使用在数组类算法题中经常考察的「二分查找」和「双指针」算法了。
@@ -518,7 +555,8 @@ comments: true
=== "C#"
```csharp title="list.cs"
-
+ /* 排序列表 */
+ list.Sort(); // 排序后,列表元素从小到大排列
```
## 列表简易实现 *
@@ -1084,5 +1122,101 @@ comments: true
=== "C#"
```csharp title="my_list.cs"
+ class MyList
+ {
+ private int[] nums; // 数组(存储列表元素)
+ private int capacity = 10; // 列表容量
+ private int size = 0; // 列表长度(即当前元素数量)
+ private int extendRatio = 2; // 每次列表扩容的倍数
+ /* 构造函数 */
+ public MyList()
+ {
+ nums = new int[capacity];
+ }
+
+ /* 获取列表长度(即当前元素数量)*/
+ public int Size()
+ {
+ return size;
+ }
+
+ /* 获取列表容量 */
+ public int Capacity()
+ {
+ return capacity;
+ }
+
+ /* 访问元素 */
+ public int Get(int index)
+ {
+ // 索引如果越界则抛出异常,下同
+ if (index >= size)
+ throw new IndexOutOfRangeException("索引越界");
+ return nums[index];
+ }
+
+ /* 更新元素 */
+ public void Set(int index, int num)
+ {
+ if (index >= size)
+ throw new IndexOutOfRangeException("索引越界");
+ nums[index] = num;
+ }
+
+ /* 尾部添加元素 */
+ public void Add(int num)
+ {
+ // 元素数量超出容量时,触发扩容机制
+ if (size == Capacity())
+ ExtendCapacity();
+ nums[size] = num;
+ // 更新元素数量
+ size++;
+ }
+
+ /* 中间插入元素 */
+ public void Insert(int index, int num)
+ {
+ if (index >= size)
+ throw new IndexOutOfRangeException("索引越界");
+ // 元素数量超出容量时,触发扩容机制
+ if (size == Capacity())
+ ExtendCapacity();
+ // 将索引 index 以及之后的元素都向后移动一位
+ for (int j = size - 1; j >= index; j--)
+ {
+ nums[j + 1] = nums[j];
+ }
+ nums[index] = num;
+ // 更新元素数量
+ size++;
+ }
+
+ /* 删除元素 */
+ public int Remove(int index)
+ {
+ if (index >= size)
+ throw new IndexOutOfRangeException("索引越界");
+ int num = nums[index];
+ // 将索引 index 之后的元素都向前移动一位
+ for (int j = index; j < size - 1; j++)
+ {
+ nums[j] = nums[j + 1];
+ }
+ // 更新元素数量
+ size--;
+ // 返回被删除元素
+ return num;
+ }
+
+ /* 列表扩容 */
+ public void ExtendCapacity()
+ {
+ // 新建一个长度为 size 的数组,并将原数组拷贝到新数组
+ System.Array.Resize(ref nums, Capacity() * extendRatio);
+ // 更新列表容量
+ capacity = nums.Length;
+ }
+ }
```
diff --git a/docs/chapter_computational_complexity/space_complexity.md b/docs/chapter_computational_complexity/space_complexity.md
index d640c501b..8ea15a2e8 100644
--- a/docs/chapter_computational_complexity/space_complexity.md
+++ b/docs/chapter_computational_complexity/space_complexity.md
@@ -149,7 +149,29 @@ comments: true
=== "C#"
```csharp title=""
+ /* 类 */
+ class Node
+ {
+ int val;
+ Node next;
+ Node(int x) { val = x; }
+ }
+ /* 函数(或称方法) */
+ int function()
+ {
+ // do something...
+ return 0;
+ }
+
+ int algorithm(int n)
+ { // 输入数据
+ int a = 0; // 暂存数据(常量)
+ int b = 0; // 暂存数据(变量)
+ Node node = new Node(0); // 暂存数据(对象)
+ int c = function(); // 栈帧空间(调用函数)
+ return a + b + c; // 输出数据
+ }
```
## 推算方法
@@ -228,7 +250,15 @@ comments: true
=== "C#"
```csharp title=""
-
+ void algorithm(int n)
+ {
+ int a = 0; // O(1)
+ int[] b = new int[10000]; // O(1)
+ if (n > 10)
+ {
+ int[] nums = new int[n]; // O(n)
+ }
+ }
```
**在递归函数中,需要注意统计栈帧空间。** 例如函数 `loop()`,在循环中调用了 $n$ 次 `function()` ,每轮中的 `function()` 都返回并释放了栈帧空间,因此空间复杂度仍为 $O(1)$ 。而递归函数 `recur()` 在运行中会同时存在 $n$ 个未返回的 `recur()` ,从而使用 $O(n)$ 的栈帧空间。
@@ -330,13 +360,31 @@ comments: true
=== "C"
```c title=""
-
+
```
=== "C#"
```csharp title=""
-
+ int function()
+ {
+ // do something
+ return 0;
+ }
+ /* 循环 O(1) */
+ void loop(int n)
+ {
+ for (int i = 0; i < n; i++)
+ {
+ function();
+ }
+ }
+ /* 递归 O(n) */
+ int recur(int n)
+ {
+ if (n == 1) return 1;
+ return recur(n - 1);
+ }
```
## 常见类型
@@ -467,7 +515,25 @@ $$
=== "C#"
```csharp title="space_complexity.cs"
-
+ /* 常数阶 */
+ void constant(int n)
+ {
+ // 常量、变量、对象占用 O(1) 空间
+ int a = 0;
+ int b = 0;
+ int[] nums = new int[10000];
+ ListNode node = new ListNode(0);
+ // 循环中的变量占用 O(1) 空间
+ for (int i = 0; i < n; i++)
+ {
+ int c = 0;
+ }
+ // 循环中的函数占用 O(1) 空间
+ for (int i = 0; i < n; i++)
+ {
+ function();
+ }
+ }
```
### 线性阶 $O(n)$
@@ -568,7 +634,24 @@ $$
=== "C#"
```csharp title="space_complexity.cs"
-
+ /* 线性阶 */
+ void linear(int n)
+ {
+ // 长度为 n 的数组占用 O(n) 空间
+ int[] nums = new int[n];
+ // 长度为 n 的列表占用 O(n) 空间
+ List nodes = new();
+ for (int i = 0; i < n; i++)
+ {
+ nodes.Add(new ListNode(i));
+ }
+ // 长度为 n 的哈希表占用 O(n) 空间
+ Dictionary map = new();
+ for (int i = 0; i < n; i++)
+ {
+ map.Add(i, i.ToString());
+ }
+ }
```
以下递归函数会同时存在 $n$ 个未返回的 `algorithm()` 函数,使用 $O(n)$ 大小的栈帧空间。
@@ -639,7 +722,13 @@ $$
=== "C#"
```csharp title="space_complexity.cs"
-
+ /* 线性阶(递归实现) */
+ void linearRecur(int n)
+ {
+ Console.WriteLine("递归 n = " + n);
+ if (n == 1) return;
+ linearRecur(n - 1);
+ }
```
![space_complexity_recursive_linear](space_complexity.assets/space_complexity_recursive_linear.png)
@@ -729,6 +818,23 @@ $$
=== "C#"
```csharp title="space_complexity.cs"
+ /* 平方阶 */
+ void quadratic(int n)
+ {
+ // 矩阵占用 O(n^2) 空间
+ int[,] numMatrix = new int[n, n];
+ // 二维列表占用 O(n^2) 空间
+ List> numList = new();
+ for (int i = 0; i < n; i++)
+ {
+ List tmp = new();
+ for (int j = 0; j < n; j++)
+ {
+ tmp.Add(0);
+ }
+ numList.Add(tmp);
+ }
+ }
```
@@ -804,6 +910,14 @@ $$
=== "C#"
```csharp title="space_complexity.cs"
+ /* 平方阶(递归实现) */
+ int quadraticRecur(int n)
+ {
+ if (n <= 0) return 0;
+ int[] nums = new int[n];
+ Console.WriteLine("递归 n = " + n + " 中的 nums 长度 = " + nums.Length);
+ return quadraticRecur(n - 1);
+ }
```
@@ -889,7 +1003,15 @@ $$
=== "C#"
```csharp title="space_complexity.cs"
-
+ /* 指数阶(建立满二叉树) */
+ TreeNode? buildTree(int n)
+ {
+ if (n == 0) return null;
+ TreeNode root = new TreeNode(0);
+ root.left = buildTree(n - 1);
+ root.right = buildTree(n - 1);
+ return root;
+ }
```
![space_complexity_exponential](space_complexity.assets/space_complexity_exponential.png)
diff --git a/docs/chapter_computational_complexity/space_time_tradeoff.md b/docs/chapter_computational_complexity/space_time_tradeoff.md
index 23c2ae7a6..651aff148 100644
--- a/docs/chapter_computational_complexity/space_time_tradeoff.md
+++ b/docs/chapter_computational_complexity/space_time_tradeoff.md
@@ -130,7 +130,23 @@ comments: true
=== "C#"
```csharp title="leetcode_two_sum.cs"
-
+ class SolutionBruteForce
+ {
+ public int[] twoSum(int[] nums, int target)
+ {
+ int size = nums.Length;
+ // 两层循环,时间复杂度 O(n^2)
+ for (int i = 0; i < size - 1; i++)
+ {
+ for (int j = i + 1; j < size; j++)
+ {
+ if (nums[i] + nums[j] == target)
+ return new int[] { i, j };
+ }
+ }
+ return new int[0];
+ }
+ }
```
### 方法二:辅助哈希表
@@ -258,5 +274,23 @@ comments: true
=== "C#"
```csharp title="leetcode_two_sum.cs"
-
+ class SolutionHashMap
+ {
+ public int[] twoSum(int[] nums, int target)
+ {
+ int size = nums.Length;
+ // 辅助哈希表,空间复杂度 O(n)
+ Dictionary dic = new();
+ // 单层循环,时间复杂度 O(n)
+ for (int i = 0; i < size; i++)
+ {
+ if (dic.ContainsKey(target - nums[i]))
+ {
+ return new int[] { dic[target - nums[i]], i };
+ }
+ dic.Add(nums[i], i);
+ }
+ return new int[0];
+ }
+ }
```
diff --git a/docs/chapter_computational_complexity/time_complexity.md b/docs/chapter_computational_complexity/time_complexity.md
index 0313c533b..cdd444eb6 100644
--- a/docs/chapter_computational_complexity/time_complexity.md
+++ b/docs/chapter_computational_complexity/time_complexity.md
@@ -97,7 +97,18 @@ $$
=== "C#"
```csharp title=""
-
+ // 在某运行平台下
+ void algorithm(int n)
+ {
+ int a = 2; // 1 ns
+ a = a + 1; // 1 ns
+ a = a * 2; // 10 ns
+ // 循环 n 次
+ for (int i = 0; i < n; i++)
+ { // 1 ns ,每轮都要执行 i++
+ Console.WriteLine(0); // 5 ns
+ }
+ }
```
但实际上, **统计算法的运行时间既不合理也不现实。** 首先,我们不希望预估时间和运行平台绑定,毕竟算法需要跑在各式各样的平台之上。其次,我们很难获知每一种操作的运行时间,这为预估过程带来了极大的难度。
@@ -212,7 +223,27 @@ $$
=== "C#"
```csharp title=""
-
+ // 算法 A 时间复杂度:常数阶
+ void algorithm_A(int n)
+ {
+ Console.WriteLine(0);
+ }
+ // 算法 B 时间复杂度:线性阶
+ void algorithm_B(int n)
+ {
+ for (int i = 0; i < n; i++)
+ {
+ Console.WriteLine(0);
+ }
+ }
+ // 算法 C 时间复杂度:常数阶
+ void algorithm_C(int n)
+ {
+ for (int i = 0; i < 1000000; i++)
+ {
+ Console.WriteLine(0);
+ }
+ }
```
![time_complexity_first_example](time_complexity.assets/time_complexity_first_example.png)
@@ -310,7 +341,15 @@ $$
=== "C#"
```csharp title=""
-
+ void algorithm(int n) {
+ int a = 1; // +1
+ a = a + 1; // +1
+ a = a * 2; // +1
+ // 循环 n 次
+ for (int i = 0; i < n; i++) { // +1(每轮都执行 i ++)
+ Console.WriteLine(0); // +1
+ }
+ }
```
$T(n)$ 是个一次函数,说明时间增长趋势是线性的,因此易得时间复杂度是线性阶。
@@ -457,7 +496,24 @@ $$
=== "C#"
```csharp title=""
-
+ void algorithm(int n)
+ {
+ int a = 1; // +0(技巧 1)
+ a = a + n; // +0(技巧 1)
+ // +n(技巧 2)
+ for (int i = 0; i < 5 * n + 1; i++)
+ {
+ Console.WriteLine(0);
+ }
+ // +n*n(技巧 3)
+ for (int i = 0; i < 2 * n; i++)
+ {
+ for (int j = 0; j < n + 1; j++)
+ {
+ Console.WriteLine(0);
+ }
+ }
+ }
```
### 2. 判断渐近上界
@@ -576,7 +632,15 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
-
+ /* 常数阶 */
+ int constant(int n)
+ {
+ int count = 0;
+ int size = 100000;
+ for (int i = 0; i < size; i++)
+ count++;
+ return count;
+ }
```
### 线性阶 $O(n)$
@@ -652,7 +716,14 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
-
+ /* 线性阶 */
+ int linear(int n)
+ {
+ int count = 0;
+ for (int i = 0; i < n; i++)
+ count++;
+ return count;
+ }
```
「遍历数组」和「遍历链表」等操作,时间复杂度都为 $O(n)$ ,其中 $n$ 为数组或链表的长度。
@@ -736,7 +807,17 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
-
+ /* 线性阶(遍历数组) */
+ int arrayTraversal(int[] nums)
+ {
+ int count = 0;
+ // 循环次数与数组长度成正比
+ foreach(int num in nums)
+ {
+ count++;
+ }
+ return count;
+ }
```
### 平方阶 $O(n^2)$
@@ -825,7 +906,20 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
-
+ /* 平方阶 */
+ int quadratic(int n)
+ {
+ int count = 0;
+ // 循环次数与数组长度成平方关系
+ for (int i = 0; i < n; i++)
+ {
+ for (int j = 0; j < n; j++)
+ {
+ count++;
+ }
+ }
+ return count;
+ }
```
![time_complexity_constant_linear_quadratic](time_complexity.assets/time_complexity_constant_linear_quadratic.png)
@@ -947,6 +1041,28 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
+ /* 平方阶(冒泡排序) */
+ int bubbleSort(int[] nums)
+ {
+ int count = 0; // 计数器
+ // 外循环:待排序元素数量为 n-1, n-2, ..., 1
+ for (int i = nums.Length - 1; i > 0; i--)
+ {
+ // 内循环:冒泡操作
+ for (int j = 0; j < i; j++)
+ {
+ if (nums[j] > nums[j + 1])
+ {
+ // 交换 nums[j] 与 nums[j + 1]
+ int tmp = nums[j];
+ nums[j] = nums[j + 1];
+ nums[j + 1] = tmp;
+ count += 3; // 元素交换包含 3 个单元操作
+ }
+ }
+ }
+ return count;
+ }
```
@@ -1048,7 +1164,22 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
-
+ /* 指数阶(循环实现) */
+ int exponential(int n)
+ {
+ int count = 0, bas = 1;
+ // cell 每轮一分为二,形成数列 1, 2, 4, 8, ..., 2^(n-1)
+ for (int i = 0; i < n; i++)
+ {
+ for (int j = 0; j < bas; j++)
+ {
+ count++;
+ }
+ bas *= 2;
+ }
+ // count = 1 + 2 + 4 + 8 + .. + 2^(n-1) = 2^n - 1
+ return count;
+ }
```
![time_complexity_exponential](time_complexity.assets/time_complexity_exponential.png)
@@ -1119,7 +1250,12 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
-
+ /* 指数阶(递归实现) */
+ int expRecur(int n)
+ {
+ if (n == 1) return 1;
+ return expRecur(n - 1) + expRecur(n - 1) + 1;
+ }
```
### 对数阶 $O(\log n)$
@@ -1205,7 +1341,17 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
-
+ /* 对数阶(循环实现) */
+ int logarithmic(float n)
+ {
+ int count = 0;
+ while (n > 1)
+ {
+ n = n / 2;
+ count++;
+ }
+ return count;
+ }
```
![time_complexity_logarithmic](time_complexity.assets/time_complexity_logarithmic.png)
@@ -1276,7 +1422,12 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
-
+ /* 对数阶(递归实现) */
+ int logRecur(float n)
+ {
+ if (n <= 1) return 0;
+ return logRecur(n / 2) + 1;
+ }
```
### 线性对数阶 $O(n \log n)$
@@ -1366,7 +1517,18 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
-
+ /* 线性对数阶 */
+ int linearLogRecur(float n)
+ {
+ if (n <= 1) return 1;
+ int count = linearLogRecur(n / 2) +
+ linearLogRecur(n / 2);
+ for (int i = 0; i < n; i++)
+ {
+ count++;
+ }
+ return count;
+ }
```
![time_complexity_logarithmic_linear](time_complexity.assets/time_complexity_logarithmic_linear.png)
@@ -1464,7 +1626,18 @@ $$
=== "C#"
```csharp title="time_complexity.cs"
-
+ /* 阶乘阶(递归实现) */
+ int factorialRecur(int n)
+ {
+ if (n == 0) return 1;
+ int count = 0;
+ // 从 1 个分裂出 n 个
+ for (int i = 0; i < n; i++)
+ {
+ count += factorialRecur(n - 1);
+ }
+ return count;
+ }
```
![time_complexity_factorial](time_complexity.assets/time_complexity_factorial.png)
@@ -1485,7 +1658,7 @@ $$
```java title="worst_best_time_complexity.java"
public class worst_best_time_complexity {
/* 生成一个数组,元素为 { 1, 2, ..., n },顺序被打乱 */
- static int[] randomNumbers(int n) {
+ int[] randomNumbers(int n) {
Integer[] nums = new Integer[n];
// 生成数组 nums = { 1, 2, 3, ..., n }
for (int i = 0; i < n; i++) {
@@ -1502,7 +1675,7 @@ $$
}
/* 查找数组 nums 中数字 1 所在索引 */
- static int findOne(int[] nums) {
+ int findOne(int[] nums) {
for (int i = 0; i < nums.length; i++) {
if (nums[i] == 1)
return i;
@@ -1511,7 +1684,7 @@ $$
}
/* Driver Code */
- public static void main(String[] args) {
+ public void main(String[] args) {
for (int i = 0; i < 10; i++) {
int n = 100;
int[] nums = randomNumbers(n);
@@ -1652,7 +1825,51 @@ $$
=== "C#"
```csharp title="worst_best_time_complexity.cs"
+ /* 生成一个数组,元素为 { 1, 2, ..., n },顺序被打乱 */
+ int[] randomNumbers(int n)
+ {
+ int[] nums = new int[n];
+ // 生成数组 nums = { 1, 2, 3, ..., n }
+ for (int i = 0; i < n; i++)
+ {
+ nums[i] = i + 1;
+ }
+ // 随机打乱数组元素
+ for (int i = 0; i < nums.Length; i++)
+ {
+ var index = new Random().Next(i, nums.Length);
+ var tmp = nums[i];
+ var ran = nums[index];
+ nums[i] = ran;
+ nums[index] = tmp;
+ }
+ return nums;
+ }
+
+ /* 查找数组 nums 中数字 1 所在索引 */
+ int findOne(int[] nums)
+ {
+ for (int i = 0; i < nums.Length; i++)
+ {
+ if (nums[i] == 1)
+ return i;
+ }
+ return -1;
+ }
+
+ /* Driver Code */
+ public void main(String[] args)
+ {
+ for (int i = 0; i < 10; i++)
+ {
+ int n = 100;
+ int[] nums = randomNumbers(n);
+ int index = findOne(nums);
+ Console.WriteLine("\n数组 [ 1, 2, ..., n ] 被打乱后 = " + string.Join(",", nums));
+ Console.WriteLine("数字 1 的索引为 " + index);
+ }
+ }
```
!!! tip
diff --git a/docs/chapter_hashing/hash_map.md b/docs/chapter_hashing/hash_map.md
index dc4f14764..cb439546a 100644
--- a/docs/chapter_hashing/hash_map.md
+++ b/docs/chapter_hashing/hash_map.md
@@ -150,7 +150,24 @@ comments: true
=== "C#"
```csharp title="hash_map.cs"
+ /* 初始化哈希表 */
+ Dictionary map = new ();
+ /* 添加操作 */
+ // 在哈希表中添加键值对 (key, value)
+ map.Add(12836, "小哈");
+ map.Add(15937, "小啰");
+ map.Add(16750, "小算");
+ map.Add(13276, "小法");
+ map.Add(10583, "小鸭");
+
+ /* 查询操作 */
+ // 向哈希表输入键 key ,得到值 value
+ String name = map[15937];
+
+ /* 删除操作 */
+ // 在哈希表中删除键值对 (key, value)
+ map.Remove(10583);
```
遍历哈希表有三种方式,即 **遍历键值对、遍历键、遍历值**。
@@ -245,7 +262,19 @@ comments: true
=== "C#"
```csharp title="hash_map.cs"
-
+ /* 遍历哈希表 */
+ // 遍历键值对 Key->Value
+ foreach (var kv in map) {
+ Console.WriteLine(kv.Key + " -> " + kv.Value);
+ }
+ // 单独遍历键 key
+ foreach (int key in map.Keys) {
+ Console.WriteLine(key);
+ }
+ // 单独遍历值 value
+ foreach (String val in map.Values) {
+ Console.WriteLine(val);
+ }
```
## 哈希函数
@@ -489,6 +518,64 @@ $$
=== "C#"
```csharp title="array_hash_map.cs"
+ /* 键值对 int->String */
+ class Entry
+ {
+ public int key;
+ public String val;
+ public Entry(int key, String val)
+ {
+ this.key = key;
+ this.val = val;
+ }
+ }
+
+ /* 基于数组简易实现的哈希表 */
+ class ArrayHashMap
+ {
+ private List bucket;
+ public ArrayHashMap()
+ {
+ // 初始化一个长度为 100 的桶(数组)
+ bucket = new ();
+ for (int i = 0; i < 100; i++)
+ {
+ bucket.Add(null);
+ }
+ }
+
+ /* 哈希函数 */
+ private int hashFunc(int key)
+ {
+ int index = key % 100;
+ return index;
+ }
+
+ /* 查询操作 */
+ public String? get(int key)
+ {
+ int index = hashFunc(key);
+ Entry? pair = bucket[index];
+ if (pair == null) return null;
+ return pair.val;
+ }
+
+ /* 添加操作 */
+ public void put(int key, String val)
+ {
+ Entry pair = new Entry(key, val);
+ int index = hashFunc(key);
+ bucket[index]=pair;
+ }
+
+ /* 删除操作 */
+ public void remove(int key)
+ {
+ int index = hashFunc(key);
+ // 置为 null ,代表删除
+ bucket[index]=null;
+ }
+ }
```
diff --git a/docs/chapter_searching/binary_search.md b/docs/chapter_searching/binary_search.md
index 7e765a67f..bdaaadc5d 100644
--- a/docs/chapter_searching/binary_search.md
+++ b/docs/chapter_searching/binary_search.md
@@ -173,7 +173,25 @@ $$
=== "C#"
```csharp title="binary_search.cs"
-
+ /* 二分查找(双闭区间) */
+ int binarySearch(int[] nums, int target)
+ {
+ // 初始化双闭区间 [0, n-1] ,即 i, j 分别指向数组首元素、尾元素
+ int i = 0, j = nums.Length - 1;
+ // 循环,当搜索区间为空时跳出(当 i > j 时为空)
+ while (i <= j)
+ {
+ int m = (i + j) / 2; // 计算中点索引 m
+ if (nums[m] < target) // 此情况说明 target 在区间 [m+1, j] 中
+ i = m + 1;
+ else if (nums[m] > target) // 此情况说明 target 在区间 [i, m-1] 中
+ j = m - 1;
+ else // 找到目标元素,返回其索引
+ return m;
+ }
+ // 未找到目标元素,返回 -1
+ return -1;
+ }
```
### “左闭右开”实现
@@ -303,7 +321,25 @@ $$
=== "C#"
```csharp title="binary_search.cs"
-
+ /* 二分查找(左闭右开) */
+ int binarySearch1(int[] nums, int target)
+ {
+ // 初始化左闭右开 [0, n) ,即 i, j 分别指向数组首元素、尾元素+1
+ int i = 0, j = nums.Length;
+ // 循环,当搜索区间为空时跳出(当 i = j 时为空)
+ while (i < j)
+ {
+ int m = (i + j) / 2; // 计算中点索引 m
+ if (nums[m] < target) // 此情况说明 target 在区间 [m+1, j) 中
+ i = m + 1;
+ else if (nums[m] > target) // 此情况说明 target 在区间 [i, m) 中
+ j = m;
+ else // 找到目标元素,返回其索引
+ return m;
+ }
+ // 未找到目标元素,返回 -1
+ return -1;
+ }
```
### 两种表示对比
@@ -383,7 +419,10 @@ $$
=== "C#"
```csharp title=""
-
+ // (i + j) 有可能超出 int 的取值范围
+ int m = (i + j) / 2;
+ // 更换为此写法则不会越界
+ int m = i + (j - i) / 2;
```
## 复杂度分析
diff --git a/docs/chapter_searching/hashing_search.md b/docs/chapter_searching/hashing_search.md
index b5537212e..a52f72e21 100644
--- a/docs/chapter_searching/hashing_search.md
+++ b/docs/chapter_searching/hashing_search.md
@@ -86,7 +86,13 @@ comments: true
=== "C#"
```csharp title="hashing_search.cs"
-
+ /* 哈希查找(数组) */
+ int hashingSearch(Dictionary map, int target)
+ {
+ // 哈希表的 key: 目标元素,value: 索引
+ // 若哈希表中无此 key ,返回 -1
+ return map.GetValueOrDefault(target, -1);
+ }
```
再比如,如果我们想要给定一个目标结点值 `target` ,获取对应的链表结点对象,那么也可以使用哈希查找实现。
@@ -163,7 +169,14 @@ comments: true
=== "C#"
```csharp title="hashing_search.cs"
+ /* 哈希查找(链表) */
+ ListNode? hashingSearch1(Dictionary map, int target)
+ {
+ // 哈希表的 key: 目标结点值,value: 结点对象
+ // 若哈希表中无此 key ,返回 null
+ return map.GetValueOrDefault(target);
+ }
```
## 复杂度分析
diff --git a/docs/chapter_searching/linear_search.md b/docs/chapter_searching/linear_search.md
index e1a4ac142..3284db06c 100644
--- a/docs/chapter_searching/linear_search.md
+++ b/docs/chapter_searching/linear_search.md
@@ -106,6 +106,19 @@ comments: true
=== "C#"
```csharp title="linear_search.cs"
+ /* 线性查找(数组) */
+ int linearSearch(int[] nums, int target)
+ {
+ // 遍历数组
+ for (int i = 0; i < nums.Length; i++)
+ {
+ // 找到目标元素,返回其索引
+ if (nums[i] == target)
+ return i;
+ }
+ // 未找到目标元素,返回 -1
+ return -1;
+ }
```
@@ -209,7 +222,20 @@ comments: true
=== "C#"
```csharp title="linear_search.cs"
-
+ /* 线性查找(链表) */
+ ListNode? linearSearch(ListNode head, int target)
+ {
+ // 遍历链表
+ while (head != null)
+ {
+ // 找到目标结点,返回之
+ if (head.val == target)
+ return head;
+ head = head.next;
+ }
+ // 未找到目标结点,返回 null
+ return null;
+ }
```
## 复杂度分析
diff --git a/docs/chapter_sorting/bubble_sort.md b/docs/chapter_sorting/bubble_sort.md
index 23f7eceed..f44b11924 100644
--- a/docs/chapter_sorting/bubble_sort.md
+++ b/docs/chapter_sorting/bubble_sort.md
@@ -176,7 +176,25 @@ comments: true
=== "C#"
```csharp title="bubble_sort.cs"
-
+ /* 冒泡排序 */
+ void bubbleSort(int[] nums)
+ {
+ // 外循环:待排序元素数量为 n-1, n-2, ..., 1
+ for (int i = nums.Length - 1; i > 0; i--)
+ {
+ // 内循环:冒泡操作
+ for (int j = 0; j < i; j++)
+ {
+ if (nums[j] > nums[j + 1])
+ {
+ // 交换 nums[j] 与 nums[j + 1]
+ int tmp = nums[j];
+ nums[j] = nums[j + 1];
+ nums[j + 1] = tmp;
+ }
+ }
+ }
+ }
```
## 算法特性
@@ -340,5 +358,26 @@ comments: true
=== "C#"
```csharp title="bubble_sort.cs"
-
+ /* 冒泡排序(标志优化)*/
+ void bubbleSortWithFlag(int[] nums)
+ {
+ // 外循环:待排序元素数量为 n-1, n-2, ..., 1
+ for (int i = nums.Length - 1; i > 0; i--)
+ {
+ bool flag = false; // 初始化标志位
+ // 内循环:冒泡操作
+ for (int j = 0; j < i; j++)
+ {
+ if (nums[j] > nums[j + 1])
+ {
+ // 交换 nums[j] 与 nums[j + 1]
+ int tmp = nums[j];
+ nums[j] = nums[j + 1];
+ nums[j + 1] = tmp;
+ flag = true; // 记录交换元素
+ }
+ }
+ if (!flag) break; // 此轮冒泡未交换任何元素,直接跳出
+ }
+ }
```
diff --git a/docs/chapter_sorting/insertion_sort.md b/docs/chapter_sorting/insertion_sort.md
index b1477213f..1614b5c35 100644
--- a/docs/chapter_sorting/insertion_sort.md
+++ b/docs/chapter_sorting/insertion_sort.md
@@ -141,7 +141,22 @@ comments: true
=== "C#"
```csharp title="insertion_sort.cs"
-
+ /* 插入排序 */
+ void insertionSort(int[] nums)
+ {
+ // 外循环:base = nums[1], nums[2], ..., nums[n-1]
+ for (int i = 1; i < nums.Length; i++)
+ {
+ int bas = nums[i], j = i - 1;
+ // 内循环:将 base 插入到左边的正确位置
+ while (j >= 0 && nums[j] > bas)
+ {
+ nums[j + 1] = nums[j]; // 1. 将 nums[j] 向右移动一位
+ j--;
+ }
+ nums[j + 1] = bas; // 2. 将 base 赋值到正确位置
+ }
+ }
```
## 算法特性
diff --git a/docs/chapter_sorting/merge_sort.md b/docs/chapter_sorting/merge_sort.md
index 55f6050cb..62ec5e47e 100644
--- a/docs/chapter_sorting/merge_sort.md
+++ b/docs/chapter_sorting/merge_sort.md
@@ -344,7 +344,48 @@ comments: true
=== "C#"
```csharp title="merge_sort.cs"
+ /**
+ * 合并左子数组和右子数组
+ * 左子数组区间 [left, mid]
+ * 右子数组区间 [mid + 1, right]
+ */
+ void merge(int[] nums, int left, int mid, int right)
+ {
+ // 初始化辅助数组
+ int[] tmp = nums[left..(right + 1)];
+ // 左子数组的起始索引和结束索引
+ int leftStart = left - left, leftEnd = mid - left;
+ // 右子数组的起始索引和结束索引
+ int rightStart = mid + 1 - left, rightEnd = right - left;
+ // i, j 分别指向左子数组、右子数组的首元素
+ int i = leftStart, j = rightStart;
+ // 通过覆盖原数组 nums 来合并左子数组和右子数组
+ for (int k = left; k <= right; k++)
+ {
+ // 若“左子数组已全部合并完”,则选取右子数组元素,并且 j++
+ if (i > leftEnd)
+ nums[k] = tmp[j++];
+ // 否则,若“右子数组已全部合并完”或“左子数组元素 < 右子数组元素”,则选取左子数组元素,并且 i++
+ else if (j > rightEnd || tmp[i] <= tmp[j])
+ nums[k] = tmp[i++];
+ // 否则,若“左子数组元素 > 右子数组元素”,则选取右子数组元素,并且 j++
+ else
+ nums[k] = tmp[j++];
+ }
+ }
+ /* 归并排序 */
+ void mergeSort(int[] nums, int left, int right)
+ {
+ // 终止条件
+ if (left >= right) return; // 当子数组长度为 1 时终止递归
+ // 划分阶段
+ int mid = (left + right) / 2; // 计算中点
+ mergeSort(nums, left, mid); // 递归左子数组
+ mergeSort(nums, mid + 1, right); // 递归右子数组
+ // 合并阶段
+ merge(nums, left, mid, right);
+ }
```
下面重点解释一下合并方法 `merge()` 的流程:
diff --git a/docs/chapter_sorting/quick_sort.md b/docs/chapter_sorting/quick_sort.md
index 8107d1825..4ec7b9ff9 100644
--- a/docs/chapter_sorting/quick_sort.md
+++ b/docs/chapter_sorting/quick_sort.md
@@ -196,6 +196,30 @@ comments: true
=== "C#"
```csharp title="quick_sort.cs"
+ /* 元素交换 */
+ void swap(int[] nums, int i, int j)
+ {
+ int tmp = nums[i];
+ nums[i] = nums[j];
+ nums[j] = tmp;
+ }
+
+ /* 哨兵划分 */
+ int partition(int[] nums, int left, int right)
+ {
+ // 以 nums[left] 作为基准数
+ int i = left, j = right;
+ while (i < j)
+ {
+ while (i < j && nums[j] >= nums[left])
+ j--; // 从右向左找首个小于基准数的元素
+ while (i < j && nums[i] <= nums[left])
+ i++; // 从左向右找首个大于基准数的元素
+ swap(nums, i, j); // 交换这两个元素
+ }
+ swap(nums, i, left); // 将基准数交换至两子数组的分界线
+ return i; // 返回基准数的索引
+ }
```
@@ -235,7 +259,7 @@ comments: true
```cpp title="quick_sort.cpp"
/* 快速排序 */
- static void quickSort(vector& nums, int left, int right) {
+ void quickSort(vector& nums, int left, int right) {
// 子数组长度为 1 时终止递归
if (left >= right)
return;
@@ -320,6 +344,18 @@ comments: true
=== "C#"
```csharp title="quick_sort.cs"
+ /* 快速排序 */
+ void quickSort(int[] nums, int left, int right)
+ {
+ // 子数组长度为 1 时终止递归
+ if (left >= right)
+ return;
+ // 哨兵划分
+ int pivot = partition(nums, left, right);
+ // 递归左子数组、右子数组
+ quickSort(nums, left, pivot - 1);
+ quickSort(nums, pivot + 1, right);
+ }
```
@@ -513,7 +549,39 @@ comments: true
=== "C#"
```csharp title="quick_sort.cs"
+ /* 选取三个元素的中位数 */
+ int medianThree(int[] nums, int left, int mid, int right)
+ {
+ // 使用了异或操作来简化代码
+ // 异或规则为 0 ^ 0 = 1 ^ 1 = 0, 0 ^ 1 = 1 ^ 0 = 1
+ if ((nums[left] > nums[mid]) ^ (nums[left] > nums[right]))
+ return left;
+ else if ((nums[mid] < nums[left]) ^ (nums[mid] < nums[right]))
+ return mid;
+ else
+ return right;
+ }
+ /* 哨兵划分(三数取中值) */
+ int partition(int[] nums, int left, int right)
+ {
+ // 选取三个候选元素的中位数
+ int med = medianThree(nums, left, (left + right) / 2, right);
+ // 将中位数交换至数组最左端
+ swap(nums, left, med);
+ // 以 nums[left] 作为基准数
+ int i = left, j = right;
+ while (i < j)
+ {
+ while (i < j && nums[j] >= nums[left])
+ j--; // 从右向左找首个小于基准数的元素
+ while (i < j && nums[i] <= nums[left])
+ i++; // 从左向右找首个大于基准数的元素
+ swap(nums, i, j); // 交换这两个元素
+ }
+ swap(nums, i, left); // 将基准数交换至两子数组的分界线
+ return i; // 返回基准数的索引
+ }
```
## 尾递归优化
@@ -547,7 +615,7 @@ comments: true
```cpp title="quick_sort.cpp"
/* 快速排序(尾递归优化) */
- static void quickSort(vector& nums, int left, int right) {
+ void quickSort(vector& nums, int left, int right) {
// 子数组长度为 1 时终止
while (left < right) {
// 哨兵划分操作
@@ -654,5 +722,25 @@ comments: true
=== "C#"
```csharp title="quick_sort.cs"
-
+ /* 快速排序(尾递归优化) */
+ void quickSort(int[] nums, int left, int right)
+ {
+ // 子数组长度为 1 时终止
+ while (left < right)
+ {
+ // 哨兵划分操作
+ int pivot = partition(nums, left, right);
+ // 对两个子数组中较短的那个执行快排
+ if (pivot - left < right - pivot)
+ {
+ quickSort(nums, left, pivot - 1); // 递归排序左子数组
+ left = pivot + 1; // 剩余待排序区间为 [pivot + 1, right]
+ }
+ else
+ {
+ quickSort(nums, pivot + 1, right); // 递归排序右子数组
+ right = pivot - 1; // 剩余待排序区间为 [left, pivot - 1]
+ }
+ }
+ }
```
diff --git a/docs/chapter_stack_and_queue/queue.md b/docs/chapter_stack_and_queue/queue.md
index 0bcc90983..f8c864fad 100644
--- a/docs/chapter_stack_and_queue/queue.md
+++ b/docs/chapter_stack_and_queue/queue.md
@@ -205,7 +205,27 @@ comments: true
=== "C#"
```csharp title="queue.cs"
+ /* 初始化队列 */
+ Queue queue = new();
+ /* 元素入队 */
+ queue.Enqueue(1);
+ queue.Enqueue(3);
+ queue.Enqueue(2);
+ queue.Enqueue(5);
+ queue.Enqueue(4);
+
+ /* 访问队首元素 */
+ int peek = queue.Peek();
+
+ /* 元素出队 */
+ int poll = queue.Dequeue();
+
+ /* 获取队列的长度 */
+ int size = queue.Count();
+
+ /* 判断队列是否为空 */
+ bool isEmpty = queue.Count() == 0;
```
## 队列实现
@@ -532,7 +552,68 @@ comments: true
=== "C#"
```csharp title="linkedlist_queue.cs"
+ /* 基于链表实现的队列 */
+ class LinkedListQueue
+ {
+ private ListNode? front, rear; // 头结点 front ,尾结点 rear
+ private int queSize = 0;
+ public LinkedListQueue()
+ {
+ front = null;
+ rear = null;
+ }
+
+ /* 获取队列的长度 */
+ public int size()
+ {
+ return queSize;
+ }
+
+ /* 判断队列是否为空 */
+ public bool isEmpty()
+ {
+ return size() == 0;
+ }
+
+ /* 入队 */
+ public void offer(int num)
+ {
+ // 尾结点后添加 num
+ ListNode node = new ListNode(num);
+ // 如果队列为空,则令头、尾结点都指向该结点
+ if (front == null)
+ {
+ front = node;
+ rear = node;
+ // 如果队列不为空,则将该结点添加到尾结点后
+ }
+ else if (rear != null)
+ {
+ rear.next = node;
+ rear = node;
+ }
+ queSize++;
+ }
+
+ /* 出队 */
+ public int poll()
+ {
+ int num = peek();
+ // 删除头结点
+ front = front?.next;
+ queSize--;
+ return num;
+ }
+
+ /* 访问队首元素 */
+ public int peek()
+ {
+ if (size() == 0 || front == null)
+ throw new Exception();
+ return front.val;
+ }
+ }
```
### 基于数组的实现
@@ -880,7 +961,61 @@ comments: true
=== "C#"
```csharp title="array_queue.cs"
+ /* 基于环形数组实现的队列 */
+ class ArrayQueue {
+ private int[] nums; // 用于存储队列元素的数组
+ private int front = 0; // 头指针,指向队首
+ private int rear = 0; // 尾指针,指向队尾 + 1
+ public ArrayQueue(int capacity) {
+ // 初始化数组
+ nums = new int[capacity];
+ }
+
+ /* 获取队列的容量 */
+ public int capacity() {
+ return nums.Length;
+ }
+
+ /* 获取队列的长度 */
+ public int size() {
+ int capacity = this.capacity();
+ // 由于将数组看作为环形,可能 rear < front ,因此需要取余数
+ return (capacity + rear - front) % capacity;
+ }
+
+ /* 判断队列是否为空 */
+ public bool isEmpty() {
+ return rear - front == 0;
+ }
+
+ /* 入队 */
+ public void offer(int num) {
+ if (size() == capacity()) {
+ Console.WriteLine("队列已满");
+ return;
+ }
+ // 尾结点后添加 num
+ nums[rear] = num;
+ // 尾指针向后移动一位,越过尾部后返回到数组头部
+ rear = (rear + 1) % capacity();
+ }
+
+ /* 出队 */
+ public int poll() {
+ int num = peek();
+ // 队头指针向后移动一位,若越过尾部则返回到数组头部
+ front = (front + 1) % capacity();
+ return num;
+ }
+
+ /* 访问队首元素 */
+ public int peek() {
+ if (isEmpty())
+ throw new Exception();
+ return nums[front];
+ }
+ }
```
## 队列典型应用
diff --git a/docs/chapter_stack_and_queue/stack.md b/docs/chapter_stack_and_queue/stack.md
index f83448d85..74f5516e7 100644
--- a/docs/chapter_stack_and_queue/stack.md
+++ b/docs/chapter_stack_and_queue/stack.md
@@ -203,7 +203,27 @@ comments: true
=== "C#"
```csharp title="stack.cs"
+ /* 初始化栈 */
+ Stack stack = new ();
+ /* 元素入栈 */
+ stack.Push(1);
+ stack.Push(3);
+ stack.Push(2);
+ stack.Push(5);
+ stack.Push(4);
+
+ /* 访问栈顶元素 */
+ int peek = stack.Peek();
+
+ /* 元素出栈 */
+ int pop = stack.Pop();
+
+ /* 获取栈的长度 */
+ int size = stack.Count();
+
+ /* 判断是否为空 */
+ bool isEmpty = stack.Count()==0;
```
## 栈的实现
@@ -520,7 +540,54 @@ comments: true
=== "C#"
```csharp title="linkedlist_stack.cs"
+ /* 基于链表实现的栈 */
+ class LinkedListStack
+ {
+ private ListNode stackPeek; // 将头结点作为栈顶
+ private int stkSize = 0; // 栈的长度
+ public LinkedListStack()
+ {
+ stackPeek = null;
+ }
+ /* 获取栈的长度 */
+ public int size()
+ {
+ return stkSize;
+ }
+
+ /* 判断栈是否为空 */
+ public bool isEmpty()
+ {
+ return size() == 0;
+ }
+
+ /* 入栈 */
+ public void push(int num)
+ {
+ ListNode node = new ListNode(num);
+ node.next = stackPeek;
+ stackPeek = node;
+ stkSize++;
+ }
+
+ /* 出栈 */
+ public int pop()
+ {
+ int num = peek();
+ stackPeek = stackPeek?.next;
+ stkSize--;
+ return num;
+ }
+
+ /* 访问栈顶元素 */
+ public int peek()
+ {
+ if (size() == 0)
+ throw new Exception();
+ return stackPeek.val;
+ }
+ }
```
### 基于数组的实现
@@ -760,7 +827,52 @@ comments: true
=== "C#"
```csharp title="array_stack.cs"
+ /* 基于数组实现的栈 */
+ class ArrayStack
+ {
+ private List stack;
+ public ArrayStack()
+ {
+ // 初始化列表(动态数组)
+ stack = new();
+ }
+ /* 获取栈的长度 */
+ public int size()
+ {
+ return stack.Count();
+ }
+
+ /* 判断栈是否为空 */
+ public bool isEmpty()
+ {
+ return size() == 0;
+ }
+
+ /* 入栈 */
+ public void push(int num)
+ {
+ stack.Add(num);
+ }
+
+ /* 出栈 */
+ public int pop()
+ {
+ if (isEmpty())
+ throw new Exception();
+ var val = peek();
+ stack.RemoveAt(size() - 1);
+ return val;
+ }
+
+ /* 访问栈顶元素 */
+ public int peek()
+ {
+ if (isEmpty())
+ throw new Exception();
+ return stack[size() - 1];
+ }
+ }
```
!!! tip
diff --git a/docs/chapter_tree/avl_tree.md b/docs/chapter_tree/avl_tree.md
index 35397f835..ab3574263 100644
--- a/docs/chapter_tree/avl_tree.md
+++ b/docs/chapter_tree/avl_tree.md
@@ -78,7 +78,14 @@ G. M. Adelson-Velsky 和 E. M. Landis 在其 1962 年发表的论文 "An algorit
=== "C#"
```csharp title="avl_tree.cs"
-
+ /* AVL 树结点类 */
+ class TreeNode {
+ public int val; // 结点值
+ public int height; // 结点高度
+ public TreeNode left; // 左子结点
+ public TreeNode right; // 右子结点
+ public TreeNode(int x) { val = x; }
+ }
```
「结点高度」是最远叶结点到该结点的距离,即走过的「边」的数量。需要特别注意,**叶结点的高度为 0 ,空结点的高度为 -1** 。我们封装两个工具函数,分别用于获取与更新结点的高度。
@@ -138,7 +145,19 @@ G. M. Adelson-Velsky 和 E. M. Landis 在其 1962 年发表的论文 "An algorit
=== "C#"
```csharp title="avl_tree.cs"
-
+ /* 获取结点高度 */
+ public int height(TreeNode? node)
+ {
+ // 空结点高度为 -1 ,叶结点高度为 0
+ return node == null ? -1 : node.height;
+ }
+
+ /* 更新结点高度 */
+ private void updateHeight(TreeNode node)
+ {
+ // 结点高度等于最高子树高度 + 1
+ node.height = Math.Max(height(node.left), height(node.right)) + 1;
+ }
```
### 结点平衡因子
@@ -196,7 +215,14 @@ G. M. Adelson-Velsky 和 E. M. Landis 在其 1962 年发表的论文 "An algorit
=== "C#"
```csharp title="avl_tree.cs"
-
+ /* 获取平衡因子 */
+ public int balanceFactor(TreeNode? node)
+ {
+ // 空结点平衡因子为 0
+ if (node == null) return 0;
+ // 结点平衡因子 = 左子树高度 - 右子树高度
+ return height(node.left) - height(node.right);
+ }
```
!!! note
@@ -285,6 +311,23 @@ AVL 树的独特之处在于「旋转 Rotation」的操作,其可 **在不影
=== "C#"
```csharp title="avl_tree.cs"
+ /* 右旋操作 */
+ TreeNode? rightRotate(TreeNode? node)
+ {
+ if (node == null)
+ return null;
+
+ TreeNode? child = node.left;
+ TreeNode? grandChild = child?.right;
+ // 以 child 为原点,将 node 向右旋转
+ child.right = node;
+ node.left = grandChild;
+ // 更新结点高度
+ updateHeight(node);
+ updateHeight(child);
+ // 返回旋转后子树的根节点
+ return child;
+ }
```
@@ -353,7 +396,23 @@ AVL 树的独特之处在于「旋转 Rotation」的操作,其可 **在不影
=== "C#"
```csharp title="avl_tree.cs"
-
+ /* 左旋操作 */
+ TreeNode? leftRotate(TreeNode? node)
+ {
+ if (node == null)
+ return null;
+
+ TreeNode? child = node.right;
+ TreeNode? grandChild = child?.left;
+ // 以 child 为原点,将 node 向左旋转
+ child.left = node;
+ node.right = grandChild;
+ // 更新结点高度
+ updateHeight(node);
+ updateHeight(child);
+ // 返回旋转后子树的根节点
+ return child;
+ }
```
### Case 3 - 先左后右
@@ -462,7 +521,47 @@ AVL 树的独特之处在于「旋转 Rotation」的操作,其可 **在不影
=== "C#"
```csharp title="avl_tree.cs"
-
+ /* 执行旋转操作,使该子树重新恢复平衡 */
+ TreeNode? rotate(TreeNode? node)
+ {
+ if (node == null)
+ return node;
+
+ // 获取结点 node 的平衡因子
+ int balanceFactorInt = balanceFactor(node);
+ // 左偏树
+ if (balanceFactorInt > 1)
+ {
+ if (balanceFactor(node.left) >= 0)
+ {
+ // 右旋
+ return rightRotate(node);
+ }
+ else
+ {
+ // 先左旋后右旋
+ node.left = leftRotate(node?.left);
+ return rightRotate(node);
+ }
+ }
+ // 右偏树
+ if (balanceFactorInt < -1)
+ {
+ if (balanceFactor(node.right) <= 0)
+ {
+ // 左旋
+ return leftRotate(node);
+ }
+ else
+ {
+ // 先右旋后左旋
+ node.right = rightRotate(node?.right);
+ return leftRotate(node);
+ }
+ }
+ // 平衡树,无需旋转,直接返回
+ return node;
+ }
```
## AVL 树常用操作
@@ -537,7 +636,30 @@ AVL 树的独特之处在于「旋转 Rotation」的操作,其可 **在不影
=== "C#"
```csharp title="avl_tree.cs"
-
+ /* 插入结点 */
+ public TreeNode? insert(int val)
+ {
+ root = insertHelper(root, val);
+ return root;
+ }
+
+ /* 递归插入结点(辅助函数) */
+ private TreeNode? insertHelper(TreeNode? node, int val)
+ {
+ if (node == null) return new TreeNode(val);
+ /* 1. 查找插入位置,并插入结点 */
+ if (val < node.val)
+ node.left = insertHelper(node.left, val);
+ else if (val > node.val)
+ node.right = insertHelper(node.right, val);
+ else
+ return node; // 重复结点不插入,直接返回
+ updateHeight(node); // 更新结点高度
+ /* 2. 执行旋转操作,使该子树重新恢复平衡 */
+ node = rotate(node);
+ // 返回子树的根节点
+ return node;
+ }
```
### 删除结点
@@ -634,7 +756,60 @@ AVL 树的独特之处在于「旋转 Rotation」的操作,其可 **在不影
=== "C#"
```csharp title="avl_tree.cs"
-
+ /* 删除结点 */
+ public TreeNode? remove(int val)
+ {
+ root = removeHelper(root, val);
+ return root;
+ }
+
+ /* 递归删除结点(辅助函数) */
+ private TreeNode? removeHelper(TreeNode? node, int val)
+ {
+ if (node == null) return null;
+ /* 1. 查找结点,并删除之 */
+ if (val < node.val)
+ node.left = removeHelper(node.left, val);
+ else if (val > node.val)
+ node.right = removeHelper(node.right, val);
+ else
+ {
+ if (node.left == null || node.right == null)
+ {
+ TreeNode? child = node.left != null ? node.left : node.right;
+ // 子结点数量 = 0 ,直接删除 node 并返回
+ if (child == null)
+ return null;
+ // 子结点数量 = 1 ,直接删除 node
+ else
+ node = child;
+ }
+ else
+ {
+ // 子结点数量 = 2 ,则将中序遍历的下个结点删除,并用该结点替换当前结点
+ TreeNode? temp = minNode(node.right);
+ node.right = removeHelper(node.right, temp.val);
+ node.val = temp.val;
+ }
+ }
+ updateHeight(node); // 更新结点高度
+ /* 2. 执行旋转操作,使该子树重新恢复平衡 */
+ node = rotate(node);
+ // 返回子树的根节点
+ return node;
+ }
+
+ /* 获取最小结点 */
+ private TreeNode? minNode(TreeNode? node)
+ {
+ if (node == null) return node;
+ // 循环访问左子结点,直到叶结点时为最小结点,跳出
+ while (node.left != null)
+ {
+ node = node.left;
+ }
+ return node;
+ }
```
### 查找结点
diff --git a/docs/chapter_tree/binary_search_tree.md b/docs/chapter_tree/binary_search_tree.md
index ff04e0622..c2551e749 100644
--- a/docs/chapter_tree/binary_search_tree.md
+++ b/docs/chapter_tree/binary_search_tree.md
@@ -159,7 +159,23 @@ comments: true
=== "C#"
```csharp title="binary_search_tree.cs"
-
+ /* 查找结点 */
+ TreeNode? search(int num)
+ {
+ TreeNode? cur = root;
+ // 循环查找,越过叶结点后跳出
+ while (cur != null)
+ {
+ // 目标结点在 root 的右子树中
+ if (cur.val < num) cur = cur.right;
+ // 目标结点在 root 的左子树中
+ else if (cur.val > num) cur = cur.left;
+ // 找到目标结点,跳出循环
+ else break;
+ }
+ // 返回目标结点
+ return cur;
+ }
```
### 插入结点
@@ -335,7 +351,33 @@ comments: true
=== "C#"
```csharp title="binary_search_tree.cs"
+ /* 插入结点 */
+ TreeNode? insert(int num)
+ {
+ // 若树为空,直接提前返回
+ if (root == null) return null;
+ TreeNode? cur = root, pre = null;
+ // 循环查找,越过叶结点后跳出
+ while (cur != null)
+ {
+ // 找到重复结点,直接返回
+ if (cur.val == num) return null;
+ pre = cur;
+ // 插入位置在 root 的右子树中
+ if (cur.val < num) cur = cur.right;
+ // 插入位置在 root 的左子树中
+ else cur = cur.left;
+ }
+ // 插入结点 val
+ TreeNode node = new TreeNode(num);
+ if (pre != null)
+ {
+ if (pre.val < num) pre.right = node;
+ else pre.left = node;
+ }
+ return node;
+ }
```
为了插入结点,需要借助 **辅助结点 `prev`** 保存上一轮循环的结点,这样在遍历到 $\text{null}$ 时,我们也可以获取到其父结点,从而完成结点插入操作。
@@ -649,7 +691,68 @@ comments: true
=== "C#"
```csharp title="binary_search_tree.cs"
-
+ /* 删除结点 */
+ TreeNode? remove(int num)
+ {
+ // 若树为空,直接提前返回
+ if (root == null) return null;
+ TreeNode? cur = root, pre = null;
+ // 循环查找,越过叶结点后跳出
+ while (cur != null)
+ {
+ // 找到待删除结点,跳出循环
+ if (cur.val == num) break;
+ pre = cur;
+ // 待删除结点在 root 的右子树中
+ if (cur.val < num) cur = cur.right;
+ // 待删除结点在 root 的左子树中
+ else cur = cur.left;
+ }
+ // 若无待删除结点,则直接返回
+ if (cur == null || pre == null) return null;
+ // 子结点数量 = 0 or 1
+ if (cur.left == null || cur.right == null)
+ {
+ // 当子结点数量 = 0 / 1 时, child = null / 该子结点
+ TreeNode? child = cur.left != null ? cur.left : cur.right;
+ // 删除结点 cur
+ if (pre.left == cur)
+ {
+ pre.left = child;
+ }
+ else
+ {
+ pre.right = child;
+ }
+ }
+ // 子结点数量 = 2
+ else
+ {
+ // 获取中序遍历中 cur 的下一个结点
+ TreeNode? nex = min(cur.right);
+ if (nex != null)
+ {
+ int tmp = nex.val;
+ // 递归删除结点 nex
+ remove(nex.val);
+ // 将 nex 的值复制给 cur
+ cur.val = tmp;
+ }
+ }
+ return cur;
+ }
+
+ /* 获取最小结点 */
+ TreeNode? min(TreeNode? root)
+ {
+ if (root == null) return root;
+ // 循环访问左子结点,直到叶结点时为最小结点,跳出
+ while (root.left != null)
+ {
+ root = root.left;
+ }
+ return root;
+ }
```
## 二叉搜索树的优势
diff --git a/docs/chapter_tree/binary_tree.md b/docs/chapter_tree/binary_tree.md
index ed4582904..e88077276 100644
--- a/docs/chapter_tree/binary_tree.md
+++ b/docs/chapter_tree/binary_tree.md
@@ -97,7 +97,13 @@ comments: true
=== "C#"
```csharp title=""
-
+ /* 链表结点类 */
+ class TreeNode {
+ int val; // 结点值
+ TreeNode left; // 左子结点指针
+ TreeNode right; // 右子结点指针
+ TreeNode(int x) { val = x; }
+ }
```
结点的两个指针分别指向「左子结点 Left Child Node」和「右子结点 Right Child Node」,并且称该结点为两个子结点的「父结点 Parent Node」。给定二叉树某结点,将左子结点以下的树称为该结点的「左子树 Left Subtree」,右子树同理。
@@ -232,7 +238,18 @@ comments: true
=== "C#"
```csharp title="binary_tree.cs"
-
+ /* 初始化二叉树 */
+ // 初始化结点
+ TreeNode n1 = new TreeNode(1);
+ TreeNode n2 = new TreeNode(2);
+ TreeNode n3 = new TreeNode(3);
+ TreeNode n4 = new TreeNode(4);
+ TreeNode n5 = new TreeNode(5);
+ // 构建引用指向(即指针)
+ n1.left = n2;
+ n1.right = n3;
+ n2.left = n4;
+ n2.right = n5;
```
**插入与删除结点。** 与链表类似,插入与删除结点都可以通过修改指针实现。
@@ -315,7 +332,13 @@ comments: true
=== "C#"
```csharp title="binary_tree.cs"
-
+ /* 插入与删除结点 */
+ TreeNode P = new TreeNode(0);
+ // 在 n1 -> n2 中间插入结点 P
+ n1.left = P;
+ P.left = n2;
+ // 删除结点 P
+ n1.left = n2;
```
!!! note
@@ -446,7 +469,9 @@ comments: true
=== "C#"
```csharp title=""
-
+ /* 二叉树的数组表示 */
+ // 使用 int?可空类型 ,就可以使用 null 来标记空位
+ int?[] tree = { 1, 2, 3, 4, null, 6, 7, 8, 9, null, null, 12, null, null, 15 };
```
![array_representation_with_empty](binary_tree.assets/array_representation_with_empty.png)
diff --git a/docs/chapter_tree/binary_tree_traversal.md b/docs/chapter_tree/binary_tree_traversal.md
index 129d297c6..971d24cc5 100644
--- a/docs/chapter_tree/binary_tree_traversal.md
+++ b/docs/chapter_tree/binary_tree_traversal.md
@@ -149,6 +149,25 @@ comments: true
=== "C#"
```csharp title="binary_tree_bfs.cs"
+ /* 层序遍历 */
+ public List hierOrder(TreeNode root)
+ {
+ // 初始化队列,加入根结点
+ Queue queue = new();
+ queue.Enqueue(root);
+ // 初始化一个列表,用于保存遍历序列
+ List list = new();
+ while (queue.Count != 0)
+ {
+ TreeNode node = queue.Dequeue(); // 队列出队
+ list.Add(node.val); // 保存结点值
+ if (node.left != null)
+ queue.Enqueue(node.left); // 左子结点入队
+ if (node.right != null)
+ queue.Enqueue(node.right); // 右子结点入队
+ }
+ return list;
+ }
```
@@ -354,6 +373,35 @@ comments: true
=== "C#"
```csharp title="binary_tree_dfs.cs"
+ /* 前序遍历 */
+ void preOrder(TreeNode? root)
+ {
+ if (root == null) return;
+ // 访问优先级:根结点 -> 左子树 -> 右子树
+ list.Add(root.val);
+ preOrder(root.left);
+ preOrder(root.right);
+ }
+
+ /* 中序遍历 */
+ void inOrder(TreeNode? root)
+ {
+ if (root == null) return;
+ // 访问优先级:左子树 -> 根结点 -> 右子树
+ inOrder(root.left);
+ list.Add(root.val);
+ inOrder(root.right);
+ }
+
+ /* 后序遍历 */
+ void postOrder(TreeNode? root)
+ {
+ if (root == null) return;
+ // 访问优先级:左子树 -> 右子树 -> 根结点
+ postOrder(root.left);
+ postOrder(root.right);
+ list.Add(root.val);
+ }
```