http://pat.zju.edu.cn/contests/pat-practise/1015

1015. Reversible Primes (20)

时间限制

400 ms

内存限制

32000 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

我好久没有看懂题目了。。这次也不例外。什么逻辑，N进制数出现了N+1？

 #include
 #include
 #include
 #include
 #include
 #include
 #include
 #include
 #include
 #include
 #include
 #include
 using namespace std;
 #define MAX 0x6fffffff
 bool isprime(int n){
     if(n==1)
         return false;
     int q = sqrt(n+0.0);
     for(int i=2;i<=q;++i){
         if(n%i==0)
             return false;
     }
     return true;
 }

 int reverse(int n, int radix){
     int ans = 0;
     while(n>0){
         ans = ans*radix + n%radix;
         n /= radix;
     }
     return ans;
 }
 int main(){

     //freopen("in.txt", "r", stdin);

     int n, d;
     while(cin>>n, n>=0){
         cin>>d;
         if(isprime(n) && isprime(reverse(n, d)))
             printf("Yes\n");
         else
             printf("No\n");
     }

    // fclose(stdin);
     return 0;
 }