uva 524 prime ring problem—

uva 524 prime ring problem——yhx

Prime Ring Problem

A ring is composed of n (even number) circles as shown in diagram. Put natural numbers into each circle separately, and the sum of numbers in two adjacent circles should be a prime.

Note: the number of first circle should always be 1.

Input

n (0 < n <= 16)

Output

The output format is shown as sample below. Each row represents a series of circle numbers in the ring beginning from 1 clockwisely and anticlockwisely. The order of numbers must satisfy the above requirements.

You are to write a program that completes above process.

 1 #include<cstdio>
 2 #include<cstring>
 3 bool prm[35],vis[20];
 4 int a[20],n;
 5 bool ck(int x)
 6 {
 7     int i;
 8     for (i=2;i*i<=x;i++)
 9       if (x%i==0) return 0;
10     return 1;
11 }
12 void dfs(int p)
13 {
14     int i,j,k,x,y,z;
15     if (p==n+1)
16     {
17         if (prm[a[n]+a[1]])
18         {
19             printf("%d",a[1]);
20             for (i=2;i<=n;i++)
21               printf(" %d",a[i]);
22             printf("
");
23         }
24         return;
25     }
26     for (i=2;i<=n;i++)
27       if (vis[i]==0&&prm[i+a[p-1]])
28       {
29           a[p]=i;
30           vis[i]=1;
31           dfs(p+1);
32           vis[i]=0;
33       }
34 }
35 int main()
36 {
37     int i,j,k,p,q,x,y,z,t;
38     bool bbb=0;
39     for (i=2;i<=35;i++)
40       prm[i]=ck(i);
41     a[1]=1;
42     t=0;
43     while (scanf("%d",&n)==1)
44     {
45         if (bbb) printf("
");
46         bbb=1;
47         memset(vis,0,sizeof(vis));
48         vis[1]=1;
49         printf("Case %d:
",++t);
50         dfs(2);
51     }
52 }

素数环。注意边界。注意每组数据间的回车（虽然题上没说）。