[PAT甲级]1015. Reversible Primes (20)(可逆素数判断)

1015. Reversible Primes (20)

原题链接
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

题目大意：

• 可逆素数判断：一个十进制数 N 在 D进制 下反转后的十进制数仍为素数，则为可逆素数
• 注意前后均为十进制，只是在D进制下反转

代码：

#include <iostream>using namespace std;bool isPrime(int n){    if(n <= 1)        return false;    for(int i=2; i*i<=n; i++){        if(n%i == 0)            return false;    }    return true;}int main(){    bool flag = true;    int n, d;    while(flag){        cin >> n;        if(n < 0)            break;        cin >> d;//进制        if(isPrime(n) == false){            cout << "No" << endl;            continue;        }        int revers = 0;//D进制下反转后的数        while(n != 0){//D进制下反转            int temp = n%d;            revers = revers*d + temp;            n /= d;        }        if(isPrime(revers) == false){            cout << "No" << endl;        }else{            cout << "Yes" << endl;        }    }    return 0;}