A1015. Reversible Primes

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

 1 #include<cstdio>
 2 #include<iostream>
 3 #include<algorithm>
 4 #include<math.h>
 5 using namespace std;
 6 int numReverse(int N, int radix){
 7     int num[50], temp, index = 0, ans = 0;
 8     do{
 9         temp = N % radix;
10         num[index++] = temp;
11         N = N / radix;
12     }while(N != 0);
13     for(int i = index - 1, P = 1; i >= 0; i--){
14         ans += num[i] * P;
15         P = P * radix;
16     }
17     return ans;
18 }
19 int isPrime(int N){
20     int sqr = (int)sqrt(N * 1.0);
21     if(N == 1)
22         return 0;
23     for(int i = 2; i <= sqr; i++){
24         if(N % i == 0)
25             return 0;
26     }
27     return 1;
28 }
29 int main(){
30     int N, D, N2;
31     while(1){
32         scanf("%d", &N);
33         if(N < 0)
34             break;
35         scanf("%d", &D);
36         int temp = numReverse(N, D);
37         if(isPrime(N) && isPrime(temp))
38             printf("Yes\n");
39         else printf("No\n");
40     }
41     cin >> N;
42     return 0;
43 }
View Code

 

总结:

1、判断素数:

int isPrime(int N){
    int sqr = (int)sqrt(N * 1.0);  //N应该转换为小数
    if(N == 1)        //当N = 1时应返回false,容易忽略,1不是素数
        return 0;
    for(int i = 2; i <= sqr; i++){   //i <= sqr; i从2开始查找
        if(N % i == 0)
            return 0;
    }
    return 1;
}

 

posted @ 2018-02-04 22:58  ZHUQW  阅读(104)  评论(0编辑  收藏  举报