PAT A1015. Reversible Primes (20)

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
-2

Sample Output:
Yes
Yes
No

思路： T=T*D+M%D;M/=D;这两句完成反转，简单粗暴

#include<cstdio>#include<iostream>#include<cmath>using namespace std;const int maxn=100010;bool isPrime(int A){    if(A<2)        return 0;    if(A==2||A==3)        return 1;    for(int i=2;i<=sqrt(A);i++){        if(A%i==0)            return 0;    }    return 1;}int main(){//  freopen("in.txt","r",stdin);//  freopen("out.txt","w",stdout);    int N,D;    int M,T;    while(cin>>N>>D&&N>0){        T=0;M=N;        while(M){            T=T*D+M%D;//直接用M完成反转             M/=D;        }        if(isPrime(N)&&isPrime(T)){            cout<<"Yes"<<endl;        }        else            cout<<"No"<<endl;    }    return 0;}