[PAT] 1015 Reversible Primes （20 分）Java

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 (<10​5​​) 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

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 * @Auther: Xingzheng Wang
 * @Date: 2019/2/20 22:41
 * @Description: pattest
 * @Version: 1.0
 */
public class PAT1015 {

    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        while (true) {
            String[] in = reader.readLine().split(" ");
            int num = Integer.parseInt(in[0]);
            if (num < 0) break;
            int indax = Integer.parseInt(in[1]);
            if (isprime(num) && isprime(reve(num,indax))) {
                System.out.println("Yes");
            }else{
                System.out.println("No");
            }
        }
    }

    private static int reve(int num, int indax) {
        StringBuilder sb = new StringBuilder(Integer.toString(num, indax)).reverse();
        return Integer.parseInt(sb.toString(), indax);
    }

    private static boolean isprime(int num){
        if(num == 1) return false;
        for (int i = 2; i <= Math.sqrt(num); i++) {
            if (num % i == 0)
                return false;
        }
        return true;
    }
}