hello-algo/codes/csharp/chapter_computational_complexity/time_complexity.cs
hpstory 56b20eff36
feat(csharp) .NET 8.0 code migration (#966)
* .net 8.0 migration

* update docs

* revert change

* revert change and update appendix docs

* remove static

* Update binary_search_insertion.cs

* Update binary_search_insertion.cs

* Update binary_search_edge.cs

* Update binary_search_insertion.cs

* Update binary_search_edge.cs

---------

Co-authored-by: Yudong Jin <krahets@163.com>
2023-11-26 23:18:44 +08:00

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/**
* File: time_complexity.cs
* Created Time: 2022-12-23
* Author: haptear (haptear@hotmail.com)
*/
namespace hello_algo.chapter_computational_complexity;
public class time_complexity {
void Algorithm(int n) {
int a = 1; // +0技巧 1
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 AlgorithmA(int n) {
Console.WriteLine(0);
}
// 算法 B 时间复杂度:线性阶
void AlgorithmB(int n) {
for (int i = 0; i < n; i++) {
Console.WriteLine(0);
}
}
// 算法 C 时间复杂度:常数阶
void AlgorithmC(int n) {
for (int i = 0; i < 1000000; i++) {
Console.WriteLine(0);
}
}
/* 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 */
int Linear(int n) {
int count = 0;
for (int i = 0; i < n; i++)
count++;
return count;
}
/* 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 */
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) */
int BubbleSort(int[] nums) {
int count = 0; // 计数器
// 外循环:未排序区间为 [0, i]
for (int i = nums.Length - 1; i > 0; i--) {
// 内循环:将未排序区间 [0, i] 中的最大元素交换至该区间的最右端
for (int j = 0; j < i; j++) {
if (nums[j] > nums[j + 1]) {
// 交换 nums[j] 与 nums[j + 1]
(nums[j + 1], nums[j]) = (nums[j], nums[j + 1]);
count += 3; // 元素交换包含 3 个单元操作
}
}
}
return count;
}
/* 指数阶(循环实现) */
int Exponential(int n) {
int count = 0, bas = 1;
// 细胞每轮一分为二,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) */
int ExpRecur(int n) {
if (n == 1) return 1;
return ExpRecur(n - 1) + ExpRecur(n - 1) + 1;
}
/* 对数阶(循环实现) */
int Logarithmic(float n) {
int count = 0;
while (n > 1) {
n /= 2;
count++;
}
return count;
}
/* 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 */
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) */
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("常数阶的操作数量 = " + count);
count = Linear(n);
Console.WriteLine("线性阶的操作数量 = " + count);
count = ArrayTraversal(new int[n]);
Console.WriteLine("线性阶(遍历数组)的操作数量 = " + count);
count = Quadratic(n);
Console.WriteLine("平方阶的操作数量 = " + 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)的操作数量 = " + count);
count = Exponential(n);
Console.WriteLine("指数阶(循环实现)的操作数量 = " + count);
count = ExpRecur(n);
Console.WriteLine("指数阶(递归实现)的操作数量 = " + count);
count = Logarithmic((float)n);
Console.WriteLine("对数阶(循环实现)的操作数量 = " + count);
count = LogRecur((float)n);
Console.WriteLine("对数阶(递归实现)的操作数量 = " + count);
count = LinearLogRecur((float)n);
Console.WriteLine("线性对数阶(递归实现)的操作数量 = " + count);
count = FactorialRecur(n);
Console.WriteLine("阶乘阶(递归实现)的操作数量 = " + count);
}
}