PAT（甲级）2019年春季考试 7-1 Sexy Primes (20 分)

Sexy primes are pairs of primes of the form (p, p+6), so-named since “sex” is the Latin word for “six”. (Quoted from http://mathworld.wolfram.com/SexyPrimes.html)

Now given an integer, you are supposed to tell if it is a sexy prime.

Input Specification:
Each input file contains one test case. Each case gives a positive integer N (≤10^8).

Output Specification:
For each case, print in a line Yes if N is a sexy prime, then print in the next line the other sexy prime paired with N (if the answer is not unique, output the smaller number). Or if N is not a sexy prime, print No instead, then print in the next line the smallest sexy prime which is larger than N.

Sample Input 1:

Sample Output 1:

Yes
41

Sample Input 2:

Sample Output 2:

No
23

题意

一个数x是“sexy prime”指的是x是质数且x-6或x+6也是质数。
给出一个数，判断这个数是不是“sexy prime”，如果是的话输出与这个数配对的另一个“sexy prime”，如果有多个就输出小的那个（也就是x-6），如果不是就输出最小的比这个数大的“sexy prime”。
代码

标题

题目未开放，代码没有在官网测试。

//if顺序 int范围 if()判断 
#include <bits/stdc++.h>
using namespace std;
bool isPrime(int n){ 
    if(n<=1)return false;
    int sqr= (int)sqrt(1.0 * n);
    for(int i=2;i<=sqr;i++){ 
      if( n % i == 0)return false;
    }
     return true;
}
int main(){ 
    int n;
    scanf("%d",&n);
    if(isPrime(n-6)){ 
        printf("Yes\n");
        printf("%d",n-6);
    }else if(isPrime(n+6)){ 
        printf("Yes\n");
        printf("%d",n+6);
    }else{ 
        for(int i=n+1;i<=100000000;i++){ 
            if(isPrime(i-6)+isPrime(i+6)){ 
                printf("No\n");
                printf("%d",i);
                break;
            }    
        }
    }
    return 0;
}