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  • 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;
    }
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  • 原文地址:https://www.cnblogs.com/handsomecui/p/5061008.html
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