1015. Reversible Primes (20)

1. Reversible Primes (20)
   时间限制
   400 ms
   内存限制
   65536 kB
   代码长度限制
   16000 B
   判题程序
   Standard
   作者
   CHEN, Yue
   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

求N在D进制下和N在D进制下的逆序是否同时是素数

#include<iostream>#include<cmath>using namespace std;int resever(int n,int d){    int sum=0;    while(n!=0)    {        sum=(n%d)+sum*d;        n/=d;    }    return sum;}bool isprime(int num){    if (num<2)        return false;    else if (num==2)        return true ;    else if (num%2==0)        return false;    else    {        int t=sqrt(num)+1;        for (int i=2;i<=t;i++)        {            if (num%i==0)                return false;        }        return true;    }}int main(){    int n,d;    while(1)    {        cin>>n;        if (n<0)            break;        cin>>d;        int res=resever(n,d);        if (isprime(n)&&isprime(res))        {            cout<<"Yes"<<endl;        }        else        {            cout<<"No"<<endl;        }    }    return 0;}