PAT 2019-3 7-1 Sexy Primes

Description:

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 (≤).

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

Keys:

• 素数

Attention:

• 这几次很爱考素数，奶一口欧拉算法，9月份考试能不能中

Code:

 /*
 SP数，P和P+6都是素数
 给定一个正整数，判断N是否为SP数，打印与他配对的另一个素数（如果不唯一，输出较小的一个
 如果N不是SP数，打印大于N的最小SP数

 1，判断i-6是否大于n
 2，n-6可能小于0,
 */
 #include<cstdio>

 bool IsPrime(long long n)
 {
     if(n <= )
         return false;
     for(long long i=; i*i<=n; i++)
         if(n%i == )
             return false;
     return true;
 }

 int main()
 {
 #ifdef ONLINE_JUDGE
 #else
     freopen("Test.txt", "r", stdin);
 #endif // ONLINE_JUDEG

     int n;
     scanf("%d",&n);
     if(IsPrime(n-) && IsPrime(n))
         printf("Yes\n%d", n-);
     else if(IsPrime(n) && IsPrime(n+))
         printf("Yes\n%d", n+);
     else
     {
         for(int i=n+; i<1e9; i++)
             if(IsPrime(i-) && IsPrime(i))
             {
                 printf("No\n%d", i->n?i-:i);
                 break;
             }
     }

     return ;
 }