PAT甲级——A1015 Reversible Primes

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 (<) and D (1), 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

其实就是将输入的数字转化为该进制的反序列，然后再转化为10进制
然后判断是否是素数即可

 #include <iostream>
 #include <math.h>
 #include <string>

 using namespace std;

 bool isPrim(int a)
 {
     if (a < )
         return false;
     int b = (int)sqrt(1.0 * a);
     for (int i = ; i <= b; ++i)
     {
         if (a%i == )
             return false;
     }
     return true;
 }

 int getReverNum(int a, int b)
 {
     string str = "";//得到反转的序列
     while (a > )
     {
         str += a % b + '';
         a /= b;
     }
     int n = ;
     for (int i = str.length() - , j = ; i >= ; --i, ++j)
         n += (str[i] - '')*pow(b, j);
     return n;
 }

 int main()
 {
     int a, b;
     while (cin >> a)
     {
         if (a < )break;
         cin >> b;
         if (isPrim(a) && isPrim(getReverNum(a,b)))
             cout << "Yes" << endl;
         else
             cout << "No" << endl;
     }
     return ;
 }