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[35],vis[20];
int a[20],n;
bool ck(int x)
{
    int i;
    for (i=2;i*i<=x;i++)
      if (x%i==0) return 0;
    return 1;
}
void dfs(int p)
{
    int i,j,k,x,y,z;
    if (p==n+1)
    {
        if (prm[a[n]+a[1]])
        {
            printf("%d",a[1]);
            for (i=2;i<=n;i++)
              printf(" %d",a[i]);
            printf("
");
        }
        return;
    }
    for (i=2;i<=n;i++)
      if (vis[i]==0&&prm[i+a[p-1]])
      {
          a[p]=i;
          vis[i]=1;
          dfs(p+1);
          vis[i]=0;
      }
}
int main()
{
    int i,j,k,p,q,x,y,z,t;
    bool bbb=0;
    for (i=2;i<=35;i++)
      prm[i]=ck(i);
    a[1]=1;
    t=0;
    while (scanf("%d",&n)==1)
    {
        if (bbb) printf("
");
        bbb=1;
        memset(vis,0,sizeof(vis));
        vis[1]=1;
        printf("Case %d:
",++t);
        dfs(2);
    }
}

素数环。注意边界。注意每组数据间的回车（虽然题上没说）。