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c++STL随机数生成器

code • 2022-5-13 • C • 阅读 27

c++STL随机数生成器,第1张

今天呢在OIwiki上看到了1个诡异的生成随机数函数：mt19937，看到之后我直接就一脸懵了，这啥玩意？？？

最开始我以为这是1个叫M.T.的人在19937/1937年发明的函数，但是再往后看，发现这个mt好像意思是梅森缠绕器（好像还有人说叫梅森旋转算法），而19937是一个质数，19937的意思是2^19937-1，随后我就随便在网上复制了一段代码，粘到DEV里面，然后我就震惊的发现，代码CE了

然后我抱着试一下的想法，又复制到了最新版VS2022上面，然后我又震惊的发现，这玩意竟然就真过了编译，生成了一个数，看完之后，我决定测试一下这个的随机性怎么样，于是就有了下面这段代码

#include 
#include 
#include 
#include 
using namespace std;
int cnt[30050];
struct val {
	int x;//下标
	int y;//数量
}all;
int main() {
	srand(time(0));
	std :: mt19937 rng(time(0));
	//1-5000,5001-10000,10001-15000,15001-20000,20001-25000,25001-30000;
	for (int i = 0; i < 1000000; i++) {
		unsigned int x = rng() % 30000 + 1;
		//unsigned int x = rand() % 30000 + 1;
		if (1 <= x && x <= 5000) cnt[1]++;
		else if (5001 <= x && x <= 10000) cnt[2]++;
		else if (10001 <= x && x <= 15000) cnt[3]++;
		else if (15001 <= x && x <= 20000) cnt[4]++;
		else if (20001 <= x && x <= 25000) cnt[5]++;
		else cnt[6]++;
	}
	cout << "第一个数：1-5000 第二个数：5001-10000 第三个数：10001-15000 第四个数：15001-20000 第五个数：20001-25000 第六个数：25001-30000" << endl;
	cout << cnt[1] << " " << cnt[2] << " " << cnt[3] << " " << cnt[4] << " " << cnt[5] << " " << cnt[6] << endl;
	memset(cnt, 0, sizeof(cnt));
	for (int i = 0; i < 1000000; i++) {
		unsigned int x = rng() % 30000 + 1;
		//unsigned int x = rand() % 30000 + 1;
		cnt[x]++;
	}
	int maxn = -1, minn = 1000050;
	for (int i = 1; i <= 30000; i++) {
		if (cnt[i] > maxn) maxn = cnt[i];
		if (cnt[i] < minn) minn = cnt[i];
	}
	cout << "maxn：在1-30000中出现最多的数，minn：在1-30000中出现最少的数" << endl;
	cout << "maxn - minn = " << maxn - minn << endl;
	long long sum1 = 0, middle, sum2 = 0;
	for (int i = 1; i <= 30000; i++) {
		sum1 += i * cnt[i];
		if (sum2 < 500000 && sum2 + cnt[i] >= 500000) middle = i + 1;
		sum2 += cnt[i];
	}
	double average = (double)sum1 / 1000000.0;
	cout << "平均数：" << average << endl;
	cout << "中位数：" << middle << endl;
	maxn = -1;
	for (int i = 1; i <= 30000; i++) if (cnt[i] > maxn) maxn = cnt[i];
	for (int i = 1; i <= 30000; i++) if (cnt[i] == maxn) all.x = i, all.y = maxn;
	cout << "众数：" << all.x;
	return 0;
}

经过n多次测试，下面就是差距最大的几组：

 

 

 可以看到，mt19937的随机性还是很不错的，分布均匀，众数很随机，平均数、中位数很接近，maxn-minn比较小，测试完随机性，我决定再测一测速度，代码就加上几行就行了

#include 
#include 
#include 
#include 
using namespace std;
int cnt[30050];
struct val {
	int x;//下标
	int y;//数量
}all;
int main() {
	srand(time(0));
	std :: mt19937 rng(time(0));
	//1-5000,5001-10000,10001-15000,15001-20000,20001-25000,25001-30000;
	for (int i = 0; i < 1000000; i++) {
		unsigned int x = rng() % 30000 + 1;
		//unsigned int x = rand() % 30000 + 1;
		if (1 <= x && x <= 5000) cnt[1]++;
		else if (5001 <= x && x <= 10000) cnt[2]++;
		else if (10001 <= x && x <= 15000) cnt[3]++;
		else if (15001 <= x && x <= 20000) cnt[4]++;
		else if (20001 <= x && x <= 25000) cnt[5]++;
		else cnt[6]++;
	}
	cout << "第一个数：1-5000 第二个数：5001-10000 第三个数：10001-15000 第四个数：15001-20000 第五个数：20001-25000 第六个数：25001-30000" << endl;
	cout << cnt[1] << " " << cnt[2] << " " << cnt[3] << " " << cnt[4] << " " << cnt[5] << " " << cnt[6] << endl;
	memset(cnt, 0, sizeof(cnt));
	for (int i = 0; i < 1000000; i++) {
		unsigned int x = rng() % 30000 + 1;
		//unsigned int x = rand() % 30000 + 1;
		cnt[x]++;
	}
	int maxn = -1, minn = 1000050;
	for (int i = 1; i <= 30000; i++) {
		if (cnt[i] > maxn) maxn = cnt[i];
		if (cnt[i] < minn) minn = cnt[i];
	}
	cout << "maxn：在1-30000中出现最多的数，minn：在1-30000中出现最少的数" << endl;
	cout << "maxn - minn = " << maxn - minn << endl;
	long long sum1 = 0, middle, sum2 = 0;
	for (int i = 1; i <= 30000; i++) {
		sum1 += i * cnt[i];
		if (sum2 < 500000 && sum2 + cnt[i] >= 500000) middle = i + 1;
		sum2 += cnt[i];
	}
	double average = (double)sum1 / 1000000.0;
	cout << "平均数：" << average << endl;
	cout << "中位数：" << middle << endl;
	maxn = -1;
	for (int i = 1; i <= 30000; i++) if (cnt[i] > maxn) maxn = cnt[i];
	for (int i = 1; i <= 30000; i++) if (cnt[i] == maxn) all.x = i, all.y = maxn;
	cout << "众数：" << all.x;
	clock_t start = clock();
	for (int i = 0; i < 10000000; i++) {
		unsigned int x = rng() % 30000 + 1;
		//unsigned int x = rand() % 30000 + 1;
	}
	cout << endl << "生成10000000个随机数的速度（ms）：" << clock() - start;
	return 0;
}

 这个时候我发现这个mt19937几乎是个O(1)的算法，我准备再测一下rand函数的性能

首先是随机性

代码：

#include 
#include 
#include 
#include 
using namespace std;
int cnt[30050];
struct val {
	int x;//下标
	int y;//数量
}all;
int main() {
	srand(time(0));
	std :: mt19937 rng(time(0));
	//1-5000,5001-10000,10001-15000,15001-20000,20001-25000,25001-30000;
	for (int i = 0; i < 1000000; i++) {
		unsigned int x = rng() % 30000 + 1;
		//unsigned int x = rand() % 30000 + 1;
		if (1 <= x && x <= 5000) cnt[1]++;
		else if (5001 <= x && x <= 10000) cnt[2]++;
		else if (10001 <= x && x <= 15000) cnt[3]++;
		else if (15001 <= x && x <= 20000) cnt[4]++;
		else if (20001 <= x && x <= 25000) cnt[5]++;
		else cnt[6]++;
	}
	cout << "第一个数：1-5000 第二个数：5001-10000 第三个数：10001-15000 第四个数：15001-20000 第五个数：20001-25000 第六个数：25001-30000" << endl;
	cout << cnt[1] << " " << cnt[2] << " " << cnt[3] << " " << cnt[4] << " " << cnt[5] << " " << cnt[6] << endl;
	memset(cnt, 0, sizeof(cnt));
	for (int i = 0; i < 1000000; i++) {
		unsigned int x = rng() % 30000 + 1;
		//unsigned int x = rand() % 30000 + 1;
		cnt[x]++;
	}
	int maxn = -1, minn = 1000050;
	for (int i = 1; i <= 30000; i++) {
		if (cnt[i] > maxn) maxn = cnt[i];
		if (cnt[i] < minn) minn = cnt[i];
	}
	cout << "maxn：在1-30000中出现最多的数，minn：在1-30000中出现最少的数" << endl;
	cout << "maxn - minn = " << maxn - minn << endl;
	long long sum1 = 0, middle, sum2 = 0;
	for (int i = 1; i <= 30000; i++) {
		sum1 += i * cnt[i];
		if (sum2 < 500000 && sum2 + cnt[i] >= 500000) middle = i + 1;
		sum2 += cnt[i];
	}
	double average = (double)sum1 / 1000000.0;
	cout << "平均数：" << average << endl;
	cout << "中位数：" << middle << endl;
	maxn = -1;
	for (int i = 1; i <= 30000; i++) if (cnt[i] > maxn) maxn = cnt[i];
	for (int i = 1; i <= 30000; i++) if (cnt[i] == maxn) all.x = i, all.y = maxn;
	cout << "众数：" << all.x;
	//clock_t start = clock();
	//for (int i = 0; i < 10000000; i++) {
		//unsigned int x = rng() % 30000 + 1;
		//unsigned int x = rand() % 30000 + 1;
	//}
	//cout << endl << "生成10000000个随机数的速度（ms）：" << clock() - start;
	return 0;
}

 

对比一下和mt19937函数，发现不论是均匀分布还是最大值-最小值，rand都要比mt19937差一大截

最后是rand的时间

代码：
 

#include 
#include 
#include 
#include 
using namespace std;
int cnt[30050];
struct val {
	int x;//下标
	int y;//数量
}all;
int main() {
	srand(time(0));
	std :: mt19937 rng(time(0));
	//1-5000,5001-10000,10001-15000,15001-20000,20001-25000,25001-30000;
	for (int i = 0; i < 1000000; i++) {
		//unsigned int x = rng() % 30000 + 1;
		unsigned int x = rand() % 30000 + 1;
		if (1 <= x && x <= 5000) cnt[1]++;
		else if (5001 <= x && x <= 10000) cnt[2]++;
		else if (10001 <= x && x <= 15000) cnt[3]++;
		else if (15001 <= x && x <= 20000) cnt[4]++;
		else if (20001 <= x && x <= 25000) cnt[5]++;
		else cnt[6]++;
	}
	cout << "第一个数：1-5000 第二个数：5001-10000 第三个数：10001-15000 第四个数：15001-20000 第五个数：20001-25000 第六个数：25001-30000" << endl;
	cout << cnt[1] << " " << cnt[2] << " " << cnt[3] << " " << cnt[4] << " " << cnt[5] << " " << cnt[6] << endl;
	memset(cnt, 0, sizeof(cnt));
	for (int i = 0; i < 1000000; i++) {
		//unsigned int x = rng() % 30000 + 1;
		unsigned int x = rand() % 30000 + 1;
		cnt[x]++;
	}
	int maxn = -1, minn = 1000050;
	for (int i = 1; i <= 30000; i++) {
		if (cnt[i] > maxn) maxn = cnt[i];
		if (cnt[i] < minn) minn = cnt[i];
	}
	cout << "maxn：在1-30000中出现最多的数，minn：在1-30000中出现最少的数" << endl;
	cout << "maxn - minn = " << maxn - minn << endl;
	long long sum1 = 0, middle, sum2 = 0;
	for (int i = 1; i <= 30000; i++) {
		sum1 += i * cnt[i];
		if (sum2 < 500000 && sum2 + cnt[i] >= 500000) middle = i + 1;
		sum2 += cnt[i];
	}
	double average = (double)sum1 / 1000000.0;
	cout << "平均数：" << average << endl;
	cout << "中位数：" << middle << endl;
	maxn = -1;
	for (int i = 1; i <= 30000; i++) if (cnt[i] > maxn) maxn = cnt[i];
	for (int i = 1; i <= 30000; i++) if (cnt[i] == maxn) all.x = i, all.y = maxn;
	cout << "众数：" << all.x;
	clock_t start = clock();
	for (int i = 0; i < 10000000; i++) {
		//unsigned int x = rng() % 30000 + 1;
		unsigned int x = rand() % 30000 + 1;
	}
	cout << endl << "生成10000000个随机数的速度（ms）：" << clock() - start;
	return 0;
}

然后后我们可以得出1个结论，rand比mt19937除了适用性外都差很多

最后介绍一下用法，就是再代码前面加上这样一行代码初始化

std :: mt19937 rng(time(0));

然后再调用rng()就行了，生成的是unsigned int的范围的随机数，如果用int会有负数

具体的就看OIWIKI吧

最后的最后，大家留个赞再走吧

欢迎分享，转载请注明来源：内存溢出

原文地址: http://outofmemory.cn/langs/868157.html

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