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

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

 

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
",cnt);
    }
    return 0;
}