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 1023 223 10-2

Sample Output:

YesYesNo

#include <iostream>#include <stdlib.h>#include <string>#include <algorithm>#include <cmath>using namespace std;bool is_prime(long n){if (n<=1){return false;}for (size_t i = 2; i <= sqrt(n); i++){if (n%i == 0){return false;}}return true;}int main(){int n, radix;while (cin>>n && n>0){cin >> radix;int nn = n;int reverse = 0;while (n){reverse = reverse*radix + n%radix;n /= radix;}if (is_prime(nn) && is_prime(reverse)){cout << "Yes"<<endl;}else{cout << "No"<<endl;}}return 0;}