PAT 甲級 1015. Reversible Primes

原題傳送門

• 題意：給定數10進制數N和進制D，将N轉化成D進制，再将D進制的數反轉，最後轉化為10進制數M，判斷N和M是否都是質數。

#include <iostream>
using namespace std;

int isPrime(int n) {
    if(n < )
        return ;
    for(int i = ; i*i <= n; ++i) {
        if(n%i == )
            return ;
    }
    return ;
}

int change(int n, int d) {
    int b[], count = ;
    while(n) {
        b[count] = n%d;
        count++;
        n /= d;
    }  // 得到的b[]正序就是轉換後的數的逆序
    int decimal = ;
    for(int i = count-; i >= ; --i) {
        int temp = ;
        for(int j = ; j < count--i; ++j) {
            temp = temp * d;
        }
        decimal = decimal + b[i] * temp;
    }
    return decimal;
}

int main(int argc, const char * argv[]) {
    int N, D;
    while(cin >> N) {
        if(N < )
            break;
        cin >> D;
        int re = change(N, D);
        if(isPrime(N) && isPrime(re))
            cout << "Yes"<<endl;
        else
            cout << "No"<<endl;
    }

    return ;
}
           

附原題：

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