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 < 2)
        return false;
    int b = (int)sqrt(1.0 * a);
    for (int i = 2; i <= b; ++i)
    {
        if (a%i == 0)
            return false;
    }
    return true;
}

int getReverNum(int a, int b)
{
    string str = "";//得到反转的序列
    while (a > 0)
    {
        str += a % b + '0';
        a /= b;
    }
    int n = 0;
    for (int i = str.length() - 1, j = 0; i >= 0; --i, ++j)
        n += (str[i] - '0')*pow(b, j);
    return n;
}

int main()
{
    int a, b;
    while (cin >> a)
    {
        if (a < 0)break;
        cin >> b;
        if (isPrim(a) && isPrim(getReverNum(a,b)))
            cout << "Yes" << endl;
        else
            cout << "No" << endl;
    }
    return 0;
}