PAT甲级【2019年3月考题】——A1156 SexyPrimes【20】

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 (≤108 10^810
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:
47
Sample Output 1:
Yes
41
Sample Input 2:
21
Sample Output 2:
No
23

【声明】

　　由于此题还未上PAT官网题库，故没有测试集，仅仅是通过了样例，若发现错误，感谢留言指正。

Solution：

　　这道题很简单，就是判断一下n 以及 n-6 或者 n+6是素数，不是的话，那就n++，直到满足要求

　　

 #include <iostream>
 using namespace std;
 bool isPrime(int x)//判断是不是素数
 {
     if (x < )
         return x >= ;
     for (int i = ; i*i <= x; ++i)
         if (x%i == )
             return false;
     return true;
 }
 int isSexyPrimes(int x)//判断满不满足题目要求
 {
     if (isPrime(x))
     {
         bool fL = isPrime(x - ), fR = isPrime(x + );
         if (fL || fR)
             return fL ? x -  : x + ;
     }
     return -;
 }
 int main()
 {
     int n;
     cin >> n;
     int res = isSexyPrimes(n);
     if (res > )
     {
         printf("Yes\n");
         printf("%d\n", res);
     }
     else
     {
         printf("No\n");
         for (int i = n + ; i < INT32_MAX; ++i)//另寻找大数，直至满足要求
         {
             if (isSexyPrimes(i) > )
             {
                 printf("%d\n", i);
                 break;
             }
         }
     }
     return ;
 }