1015 Reversible Primes (20point(s))
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<bits/stdc++.h>
using namespace std;
int num[100];
bool isPrime(int n){
if(n<=1) return false;
for(int i=2;i*i<=n;++i)
if(n%i==0) return false;
return true;
}
int convert(int n,int radix){
int i=0;
do{
num[i++]=n%radix;
n/=radix;
}while(n);
int ans=0;
for(int j=0;j<i;++j)
ans=ans*radix+num[j];
return ans;
}
int main(){
int n,d;
while(~scanf("%d",&n)&&n>0){
scanf("%d",&d);
if(isPrime(n)){
if(isPrime(convert(n,d))){
cout<<"Yes"<<endl;
continue;
}
}
cout<<"No"<<endl;
}
}