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.

#include 
#include 
#include 
using namespace std;

bool isPrime(int x) {
    if(x < 2) {
        return false;
    }
    if(x == 2 || x == 3) {
        return true;
    }
    for(int i=2; i*i<=x; i++) {
        if(x % i == 0) {
            return false;
        }
    }
    return true;
}

int main() {
    int n, d;
    while(cin>>n) {
        if(n < 0) {
            break;
        } else {
            cin>>d;
            if(isPrime(n)) {
                queue q;
                while(n!=0) {
                    q.push(n%d);
                    n /= d;
                }
                int reverse = 0;
                while(!q.empty()) {
                    reverse=reverse*d;
                    reverse=reverse+q.front();
                    q.pop();
                }
                if(isPrime(reverse)) {
                    cout<<"Yes"<