PAT-A-1013-Reversible Primes

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:

Sample Output:

1
2
3

Yes
Yes
No

Code

#include <iostream>
#include <cmath>
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 change[200];	
	int n,d,count;
    while(scanf("%d",&n)!=EOF){
        if(n<0)break;
        scanf("%d",&d);
        if(isPrime(n)){
            count=0;
            //进行进制转化(按照从左到右低位到高位的存储)
            do{
                change[count++]=n%d;
                n/=d;
            }while(n!=0);
            //转为10进制
            int product=1;
            for(int i=count-1;i>=0;i--){
                n+=change[i]*product;
                product*=d;
            }

            if(isPrime(n))
                printf("Yes\n");
            else
                printf("No\n");
        }else
            printf("No\n");
    }
	return 0;
}