HDU 2138：How many prime numbers 【水】

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本文介绍了一种通过算法计算给定正整数中素数数量的方法。输入一系列不超过32位的正整数，程序将输出这些整数中有多少个是素数。使用了基本的素数判断方法，即检查每个数是否只能被1和它本身整除。

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How many prime numbers

Time Limit: 3000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 14709 Accepted Submission(s): 5106

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

AC-code:

#include<cstdio>
#include<cmath>
int main()
{
	int n,ans,a,i,flag;
	while(scanf("%d",&n)!=EOF)
	{
		ans=0;
		while(n--)
		{
			flag=0;
			scanf("%d",&a);
			int k=sqrt(a);
			for(i=2;i<=k;i++)
				if(a%i==0)
				{
					flag=1;
					break;
				}
			if(!flag)
				ans++;
		}
		printf("%d\n",ans);
	}
	return 0;
 }