PAT1007打卡-0911

#include <iostream>

#include <cmath>

using namespace std;

bool sushu(int n)

{

    if (n <= 3) {

        return n > 1;

    }

    int b=sqrt(n);

    for (int i = 2; i <=b; i++) {

        if(n % i == 0) {

            return false;

        }

    }

    return true;

}

int main()

{

int N;

int num=0;

cin>>N;

int su[100000];

int j=0;

for(int i=2;i<=N;i++)

{

if(sushu(i)==true)

{

su[j]=i;

j++;

}

}

for(int i=0;i<j-1;i++)

{

if(su[i+1]-su[i]==2)

num++;

}

cout<<num;

return 0;

} 

//重点在素数优化，可参考以下csdn文章：

https://blog.csdn.net/afei__/article/details/80638460?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522159981038319725264609657%2522%252C%2522scm%2522%253A%252220140713.130102334..%2522%257D&request_id=159981038319725264609657&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~all~first_rank_ecpm_v3~pc_rank_v2-4-80638460.first_rank_ecpm_v3_pc_rank_v2&utm_term=%E5%88%A4%E6%96%AD%E4%B8%80%E4%B8%AA%E6%95%B0%E6%98%AF%E5%90%A6%E4%B8%BA%E7%B4%A0%E6%95%B0&spm=1018.2118.3001.4187