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不同时间复杂度的运行时间对比

jjt二向箔 2022-01-15 阅读 96
c++
#include<iostream>
#include<chrono>
#include<thread>
using namespace std;
using namespace chrono;

//四个函数:时间复杂度分别为O(n)、O(n²)、O(nlogn)、O(logn)
//n
void function1(int n) {
	int k = 0;
	for (int i = 0; i < n; i++)
	{
		k++;
	}
}

//n²
void function2(int n) {
	int k = 0;
	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < n; j++)
		{
			k++;
		}
	}
}

//nlogn
void function3(int n) {
	int k = 0;
	for (int i = 0; i < n; i++)
	{
		for (int j = 1; j < n; j=j*2)
		{
			k++;
		}
	}
}

//logn
void function4(int n) {
	int k = 0;
	for (int i = 1; i < n; i = i * 2)
	{
		k++;
	}
}

int main() {
	int n;//数据规模
	while (true)
	{
		cout << "输入n:";
		cin >> n;

		int k;
		cout << "输入运算模式:" << "\n"
			<< "1.n" << "\n"
			<< "2.n*n" << "\n"
			<< "3.nlogn" << "\n"
			<< "4.logn" << "\n";

		cin >> k;

		milliseconds start_time = duration_cast<milliseconds>(
			system_clock::now().time_since_epoch()
			);

		switch (k)
		{
		case 1:function1(n);//O(n)
			break;
		case 2:function2(n);//O(n²)
			break;
		case 3:function3(n);//O(nlogn)
			break;
		case 4:function4(n);//O(logn)
			break;
		default:
			break;
		}
	
		milliseconds end_time = duration_cast<milliseconds>(
			system_clock::now().time_since_epoch()
			);

		cout << "耗时:" << milliseconds(end_time).count() - start_time.count() << "ms" << endl;

	}
}
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