1015. Reversible Primes

标签：c++   pat   

A reversible prime in any number system is a prime whose "reverse" in that number system is also a prime. For example in the decimal system 73 is a reversible prime because its reverse 37 is also a prime.

Now given any two positive integers N (< 10⁵) and D (1 < D <= 10), you are supposed to tell if N is a reversible prime with radix D.

Input Specification:

The input file consists of several test cases. Each case occupies a line which contains two integers N and D. The input is finished by a negative N.

Output Specification:

For each test case, print in one line "Yes" if N is a reversible prime with radix D, or "No" if not.

题目是说素数n在radix进制下反转后的数在十进制下也是素数

23是素数，二进制表示10111，反转11101，十进制数是29，纠结死我了

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

bool Isprime(int num)
{
     if(num==2) return true;
     if(num<2) return false;
     int temp=(int)sqrt(num*1.0);
     for( int i=2;i<=temp;i++) if(num%i==0) return false;
     return true;
     }
int main ()
{
    int d,n;
    while (scanf("%d",&n)&&n>=0)
    {
          int revers[100000],i=0,num=0;
          scanf("%d",&d);
          if( Isprime(n))
          {
              while( n)
              {
                   revers[i++]=n%d;
                   n=n/d;
                   //printf("%d",revers[i-1]);
                   }
              for( int j=0;j<i-1;j++)
              {
                   num=(revers[j]+num)*d;
                   }
              num+=revers[i-1];
              //printf("\n%d",num);
              if( Isprime(num)) printf("Yes\n");
              else printf("No\n");
              }
          else printf("No\n");
          }
    system("pause");
    return 0;
    }

1015. Reversible Primes

标签：c++   pat   

原文地址：http://blog.csdn.net/lchinam/article/details/43988715