题目:

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 (<) and D (1), 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 1023 223 10-2

Sample Output:

YesYesNo

分析:

进制转换，一个注意点：1不是素数，不然会卡在第二个测试点

代码:

1 #include
     
       2 #include
      
        3 using namespace std; 4 long long x; 5 int n,d; 6 bool judge(long long x){    //判断是否为素数  7     int i; 8     for(i=2;i<=sqrt(x);i++){ 9         if(x%i==0){10             break;11         }12     }13     if(i>sqrt(x)&&x>=2){14         return true;15     }else{16         return false;17     }18 }19 int main(){20     while(cin>>n&&n>=0){21         cin>>d;22         x=0;23         if(!judge(n)){24             cout<<"No"<