判断有多少个素数

最新推荐文章于 2022-08-10 10:59:53 发布

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该程序用于计算输入的整数序列中素数的数量。对于每个大于6的数，它检查是否满足6n+1或6n+5的形式，并通过判断是否有其他数能整除来确认是否为素数。对于小于等于6的数，直接判断是否为2、3或5。最终输出素数的总数。

Problem Description
Give you a lot of positive integers, just to find out how many prime numbers there are.
Input
There are a lot of cases. In each case, there is an integer N representing the number of integers to find. Each integer won’t exceed 32-bit signed integer, and each of them won’t be less than 2.
Output
For each case, print the number of prime numbers you have found out.
Sample Input
3
2 3 4
Sample Output
2
这里利用了素数一定满足6n+1或者6n+5进行剪枝

#include <iostream>
#include<math.h>
using namespace std;
int main()
{
    long long n, num;
	long long count = 0;
	while (cin>>n)
	{
		count = 0;
		long long x = n;
		while (x--)
		{
			cin >> num;
			bool flag = false;
			if (num <= 6)
			{
				if (num == 2|| num == 3||num==5)
				{
					count++;
					break;
				}
			}
			else
			if ((num + 1) % 6 == 0 || (num + 5) % 6 == 0) {
				for (long long i = 2; i < sqrt(num) + 1; i++)
				{
					if (num % i == 0 && num != i)
					{
						flag = true;
						break;
					}
				}
				if(flag==false)
				  count++;
			}
		}
		cout << count << endl;
	}
}