HDU-1016-Prime Ring Problem

 1 #include <iostream>
 2 using namespace std;
 3 int a[20];
 4 bool isprime[38] = {
 5     0,1, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1
 6 };
 7 
 8 void print(int n)
 9 {
10     for (int i = 0; i < n; i++)
11     {
12         if (i==0)
13         printf("%d", a[i]);
14         else
15         {
16             printf(" %d", a[i]);
17         }
18     }
19     printf("\n");
20 }
21 bool ok(int cur)
22 {
23     if (!isprime[a[cur] + a[cur - 1]])
24         return false;
25     for (int i = 1; i < cur; i++)
26     {
27         if (a[i] == a[cur])
28             return false;
29     }
30     return true;
31 }
32 void dfs(int n, int cur)
33 {
34     if (n & 1)
35         return;
36     if (cur == n)
37     {
38         if (isprime[1 + a[cur - 1]])
39             print(n);
40     }
41     else
42     {
43         for (int i = 2; i <= n; i++)
44         {
45             a[cur] = i;
46             if (ok(cur))
47                 dfs(n, cur + 1);
48         }
49     }
50 }
51 int main()
52 {
53     int n,k=0;
54     while (cin >> n)
55     {
56         k++;
57         printf("Case %d:\n", k);
58         a[0] = 1;
59         dfs(n, 1);
60         printf("\n");
61     }
62     return 0;
63 }