feat(csharp): add binary search csharp codes (#676)

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hpstory 2023-08-06 23:16:02 +08:00 committed by GitHub
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/**
* File: binary_search_edge.cs
* Created Time: 2023-08-06
* Author: hpstory (hpstory1024@163.com)
*/
namespace hello_algo.chapter_searching;
public class binary_search_edge {
/* 二分查找最左一个 target */
public int binarySearchLeftEdge(int[] nums, int target) {
// 等价于查找 target 的插入点
int i = binary_search_insertion.binarySearchInsertion(nums, target);
// 未找到 target ,返回 -1
if (i == nums.Length || nums[i] != target) {
return -1;
}
// 找到 target ,返回索引 i
return i;
}
/* 二分查找最右一个 target */
public int binarySearchRightEdge(int[] nums, int target) {
// 转化为查找最左一个 target + 1
int i = binary_search_insertion.binarySearchInsertion(nums, target + 1);
// j 指向最右一个 target i 指向首个大于 target 的元素
int j = i - 1;
// 未找到 target ,返回 -1
if (j == -1 || nums[j] != target) {
return -1;
}
// 找到 target ,返回索引 j
return j;
}
[Test]
public void Test() {
// 包含重复元素的数组
int[] nums = { 1, 3, 6, 6, 6, 6, 6, 10, 12, 15 };
Console.WriteLine("\n数组 nums = " + nums.PrintList());
// 二分查找左边界和右边界
foreach (int target in new int[] { 6, 7 }) {
int index = binarySearchLeftEdge(nums, target);
Console.WriteLine("最左一个元素 " + target + " 的索引为 " + index);
index = binarySearchRightEdge(nums, target);
Console.WriteLine("最右一个元素 " + target + " 的索引为 " + index);
}
}
}

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/**
* File: binary_search_insertion.cs
* Created Time: 2023-08-06
* Author: hpstory (hpstory1024@163.com)
*/
namespace hello_algo.chapter_searching;
public class binary_search_insertion {
/* 二分查找插入点(无重复元素) */
public int binarySearchInsertionSimple(int[] nums, int target) {
int i = 0, j = nums.Length - 1; // 初始化双闭区间 [0, n-1]
while (i <= j) {
int m = i + (j - i) / 2; // 计算中点索引 m
if (nums[m] < target) {
i = m + 1; // target 在区间 [m+1, j] 中
} else if (nums[m] > target) {
j = m - 1; // target 在区间 [i, m-1] 中
} else {
return m; // 找到 target ,返回插入点 m
}
}
// 未找到 target ,返回插入点 i
return i;
}
/* 二分查找插入点(存在重复元素) */
public static int binarySearchInsertion(int[] nums, int target) {
int i = 0, j = nums.Length - 1; // 初始化双闭区间 [0, n-1]
while (i <= j) {
int m = i + (j - i) / 2; // 计算中点索引 m
if (nums[m] < target) {
i = m + 1; // target 在区间 [m+1, j] 中
} else if (nums[m] > target) {
j = m - 1; // target 在区间 [i, m-1] 中
} else {
j = m - 1; // 首个小于 target 的元素在区间 [i, m-1] 中
}
}
// 返回插入点 i
return i;
}
[Test]
public void Test() {
// 无重复元素的数组
int[] nums = { 1, 3, 6, 8, 12, 15, 23, 26, 31, 35 };
Console.WriteLine("\n数组 nums = " + nums.PrintList());
// 二分查找插入点
foreach (int target in new int[] { 6, 9 }) {
int index = binarySearchInsertionSimple(nums, target);
Console.WriteLine("元素 " + target + " 的插入点的索引为 " + index);
}
// 包含重复元素的数组
nums = new int[] { 1, 3, 6, 6, 6, 6, 6, 10, 12, 15 };
Console.WriteLine("\n数组 nums = " + nums.PrintList());
// 二分查找插入点
foreach (int target in new int[] { 2, 6, 20 }) {
int index = binarySearchInsertion(nums, target);
Console.WriteLine("元素 " + target + " 的插入点的索引为 " + index);
}
}
}

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/** /**
* File: binary_search_edge.java * File: binary_search_insertion.java
* Created Time: 2023-08-04 * Created Time: 2023-08-04
* Author: Krahets (krahets@163.com) * Author: Krahets (krahets@163.com)
*/ */