1015. Reversible Primes (20)-PAT

1015. 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

推荐指数 ※

题目的意思是有一个10进制数N，让你判断以D为基数翻转后的N’，判断N和N‘是不是素数。注意原始N 不要进行进制转换。

#include<iostream>
#include<math.h>
using namespace std;
long resver_num(int n,int rd)
{
long x;
x=n%rd;
while(n/rd>0){
n=n/rd;
x=x*rd+n%rd;
}
return x;
}
bool is_prime(long x){
int i;
if(x==1)
return false;
for(i=2;i<=pow(x,0.5);i++){
if(x%i==0)
return false;
}
return true;
}
int main()
{
int n,d;
long x,y;
cin>>n;
while(n>=0){
cin>>d;
y=resver_num(n,d);
if(is_prime(n)&&is_prime(y))
cout<<"Yes"<<endl;
else
cout<<"No"<<endl;
cin>>n;
}
return 0;
}