埃拉托色尼筛法 素数

运行时间和下式成正比：N+N/2+N/3+N/7+N/11+……

#include <cstdio>
#include <cstdlib>
using namespace std;
int main(int argc, char* argv[])
{
	int n;
	if (argc != 2)
	{
		printf("usage:bin n
");
		exit(0);
	}
	n = atoi(argv[1]);
	int i;
	int* arr = (int *)malloc(sizeof(int)*(n+1));
	for (i = 0; i <= n; i++)
		arr[i] = 1;
	int j;
	for (i = 2; i <= n; i++)
	{
		if (arr[i]!=0)
			for (j = i; j*i <= n;j++)
				arr[i*j] = 0;
	}
	for (i = 2; i <= n;i++)
		if (arr[i])
			printf("%d ",i);
	printf("
");

	return 0;
}

指定参数为100后，得到100以内的质数，如下：