A1015

1015 Reversible Primes (20分)

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<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
int prime(int x){
    if(x<2)return 0;
    for(int i=2;i*i<=x;i++){
        if(x%i==0)return 0;
    }
    return 1;
}
int change(int x,int d){
    vector<int>num;
    while(x){
        num.push_back(x%d);
        x/=d;
    }
    int sum=0;
    for(int i=0;i<num.size();i++)
        sum=sum*d+num[i];
    if(prime(sum))return 1;
    else return 0;
}
int main(){
    int n,d;
    while(1){
        cin>>n>>d;
        if(n<0)return 0;
        if(prime(n)&&change(n,d))
            cout<<"Yes"<<endl;
        else cout<<"No"<<endl;
    }
}