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？

[cpp]  view plain copy

1. #include<iostream>  
2. #include<cstdio>  
3. #include<memory.h>  
4. #include<algorithm>  
5. #include<cstring>  
6. #include<queue>  
7. #include<cmath>  
8. #include<vector>  
9. #include<cstdlib>  
10. #include<cmath>  
11. #include<iomanip>  
12. #include<string>  
13. using namespace std;  
14. #define MAX 0x6fffffff  
15. bool isprime(int n){  
16.     if(n==1)  
17.         return false;  
18.     int q = sqrt(n+0.0);  
19.     for(int i=2;i<=q;++i){  
20.         if(n%i==0)  
21.             return false;  
22.     }  
23.     return true;  
24. }  
25.   
26. int reverse(int n, int radix){  
27.     int ans = 0;  
28.     while(n>0){  
29.         ans = ans*radix + n%radix;  
30.         n /= radix;  
31.     }  
32.     return ans;  
33. }  
34. int main(){  
35.   
36.     //freopen("in.txt", "r", stdin);  
37.       
38.     int n, d;  
39.     while(cin>>n, n>=0){  
40.         cin>>d;  
41.         if(isprime(n) && isprime(reverse(n, d)))  
42.             printf("Yes\n");  
43.         else  
44.             printf("No\n");  
45.     }  
46.       
47.    // fclose(stdin);  
48.     return 0;  
49. }  
50.