1015. Reversible Primes (20)

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.

Sample Input:
73 10
23 2
23 10
-2
Sample Output:
Yes
Yes
No

#include<cstdio>bool isPrime(int x){    bool flag=true;    if(x==1){        flag=false;    }    for(int i=2;i*i<=x;i++){        if(x%i==0){            flag=false;            break;        }    }    return flag;}int num[110];int main(){    int n,d;    while(scanf("%d",&n)!=EOF){        if(n<0) break;        scanf("%d",&d);        if(isPrime(n)==false){            printf("No\n");        }else{            int len=0;            do{                num[len++]=n%d;                n/=d;            }while(n);            int rev=0;            for(int i=0;i<len;i++){                rev=rev*d+num[i];            }            if(isPrime(rev)==true){                printf("Yes\n");            }else{                printf("No\n");            }        }    }    return 0;}