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.

 #include<cstdio>
 #include<cstring>
 bool prm[],vis[];
 int a[],n;
 bool ck(int x)
 {
     int i;
     for (i=;i*i<=x;i++)
       if (x%i==) return ;
     return ;
 }
 void dfs(int p)
 {
     int i,j,k,x,y,z;
     if (p==n+)
     {
         if (prm[a[n]+a[]])
         {
             printf("%d",a[]);
             for (i=;i<=n;i++)
               printf(" %d",a[i]);
             printf("\n");
         }
         return;
     }
     for (i=;i<=n;i++)
       if (vis[i]==&&prm[i+a[p-]])
       {
           a[p]=i;
           vis[i]=;
           dfs(p+);
           vis[i]=;
       }
 }
 int main()
 {
     int i,j,k,p,q,x,y,z,t;
     bool bbb=;
     for (i=;i<=;i++)
       prm[i]=ck(i);
     a[]=;
     t=;
     while (scanf("%d",&n)==)
     {
         if (bbb) printf("\n");
         bbb=;
         memset(vis,,sizeof(vis));
         vis[]=;
         printf("Case %d:\n",++t);
         dfs();
     }
 }

素数环。注意边界。注意每组数据间的回车（虽然题上没说）。