pat 1015 Reversible Primes（20 分）

Posted 2021-01-03 getcharzp

1015 Reversible Primes（20 分）

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 (<10?5??) 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 <map>
 2 #include <set>
 3 #include <queue>
 4 #include <cmath>
 5 #include <stack>
 6 #include <vector>
 7 #include <string>
 8 #include <cstdio>
 9 #include <cstring>
10 #include <climits>
11 #include <iostream>
12 #include <algorithm>
13 #define wzf ((1 + sqrt(5.0)) / 2.0)
14 #define INF 0x3f3f3f3f
15 #define LL long long
16 using namespace std;
17 
18 const int MAXN = 1e4 + 10;
19 
20 int n, r;
21 
22 bool is_prime(int n)
23 {
24     if (n == 0 || n == 1) return false;
25     for (int i = 2; i * i <= n; ++ i)
26         if (n % i == 0) return false;
27     return true;
28 }
29 
30 int main()
31 {
32     while (scanf("%d", &n), n >= 0)
33     {
34         scanf("%d", &r);
35         if (!is_prime(n))
36         {
37             printf("No
");
38             continue;
39         }
40         int cnt = 0, ans = 0;
41         stack <int> my_stack;
42         while (n)
43         {
44             my_stack.push(n % r);
45             n /= r;
46         }
47         while (my_stack.size())
48         {
49             ans += my_stack.top() * (pow(r, cnt));
50             ++ cnt;
51             my_stack.pop();
52         }
53         if (!is_prime(ans))
54             printf("No
");
55         else
56             printf("Yes
");
57     }
58     return 0;
59 }