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:
73 10
23 2
23 10
-2
Sample Output:
Yes
Yes
No
#include<cstdio>
#include<algorithm>
#include<cmath>
bool isprime(int n) {
if (n <= 1) return false;
int sqr = (int)sqrt(1.0*n);
for (int i = 2; i <=sqr; i++) {
if (n%i == 0) return false;
}
return true;
}
int rev(int n,int rad) {
int a[111] = { 0 };
int i = 0,s=0;
do {
a[i++] = n % rad;
n /= rad;
} while (n);
//for (int p = 0; p < i; p++) printf("%d ", a[p]);
//printf("\n");
for (int j = 0; j < i; j++) {
s = s * rad + a[j];
}
return s;
}
int main() {
int n, rad,n1=0;
while (scanf("%d", &n) != EOF) {
if (n<0) break;
scanf("%d", &rad);
n1 = rev(n, rad);
//printf("%d", n1);
if (!isprime(n)) printf("No\n");
else {
if (isprime(n1))
printf("Yes\n");
else
printf("No\n");
}
}
return 0;
}