1015 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 (<10^5^) 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:
1
2
3
4
73 10
23 2
23 10
-2

Sample Output:
1
2
3
Yes
Yes
No

浅析
送分题

Code
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
#include
#include
using namespace std;
bool isprime(int n) {
if(n <= 1) return false;
int sqr = int(sqrt(n * 1.0));
for(int i = 2; i <= sqr; i++) {< span>
if(n % i == 0)
return false;
}
return true;
}

bool isprime_reverse(int n,int d){
int len = 0, arr[100];
do{
arr[len++] = n % d;
n = n / d;
}while(n != 0);
for(int i = 0; i < len; i++)
n = n * d + arr[i];
return isprime(n);
}
int main() {
int n, d;
while(scanf("%d", &n) != EOF) {
if(n < 0) break;
scanf("%d", &d);
if(isprime(n) == false) {
printf("No\n");
continue;
}
if(isprime_reverse(n,d))
printf("Yes\n");
else printf("No\n");
}
return 0;
}