题目信息：
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 -2Sample Output:
Yes Yes No
代码如下：
#include <stdio.h>
#include <math.h>
int is_prime(int n) //素数判断
{
if (1 == n)
return 0;
int end = sqrt((double)n);
for (int i = 2; i <= end; ++i)
{
if (n%i == 0)
return 0;
}
return 1;
}
int re(int a, int radix) //按radix进制反转
{
int arr[20], loc = 0, s = 0, base = 1;
while (a)
{
arr[loc++] = a % radix;
a /= radix;
}
while (loc--)
{
s += arr[loc] * base;
base *= radix;
}
return s;
}
int main()
{
int a, b;
while (scanf("%d", &a) && a > 0)
{
scanf("%d", &b);
if (is_prime(a) && is_prime(re(a, b)))
printf("Yes\n");
else
printf("No\n");
}
return 0;
}
1015. Reversible Primes (20) ——PAT (Advanced Level) Practise
原文：http://blog.csdn.net/xianyun2009/article/details/39557945