How many prime numbers（求素数个数）

How many prime numbers

Time Limit: 3000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others) Total Submission(s): 14684 Accepted Submission(s): 5091

[align=left]Problem Description[/align]
Give you a lot of positive integers, just to find out how many prime numbers there are.

[align=left]Input[/align]
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.

[align=left]Output[/align]
For each case, print the number of prime numbers you have found out.

[align=left]Sample Input[/align]

3
2 3 4

[align=left]Sample Output[/align]

2

题解：

水暴力，打表不行，由于数据量太大，运行到sqrt(x)就可以；

代码：

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
bool js(int x){
if(x==2)return true;
if(x==1||x==0)return false;
if(x%2==0)return false;
for(int i=3;i<=sqrt(x);i+=2){
if(x%i==0)return false;
}
return true;
}
int main(){
int N,a;
while(~scanf("%d",&N)){
int cnt=0;
for(int i=0;i<N;i++){
scanf("%d",&a);
if(js(a))cnt++;
}
printf("%d\n",cnt);
}
return 0;
}