Prime Ring Problem

#include<stdio.h>
#include<string.h>

int prime[38]={0,0,1,1,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,0,0,0,0,1,0,1,0,0,0,0,0,1};
int visit[21],result[21];
int n;

int dfs(int num)
{
    int print(int m);
    int i;
    if(num==n && prime[result[num]+result[1]])
        print(num);
    else
    {
        for(i=2;i<=n;i++)
        {
            if(prime[result[num]+i] && !visit[i])
            {
                result[num+1]=i;
                visit[i]=1;
                dfs(num+1);
                visit[i]=0;
            }
        }
    }
    return 0;
}

int print(int m)
{
    int i;
    printf("%d",result[1]);
    for(i=2;i<=m;i++)
        printf(" %d",result[i]);
    printf("\n");
    return 0;
}

int main()
{
    int i=1;
    while(scanf("%d",&n)==1)
    {
        printf("Case %d:\n",i++);
        memset(visit,0,sizeof(visit));
        visit[1]=1;
        result[1]=1;
        dfs(1);
        printf("\n");
    }
    return 0;
}

//主要是利用深搜算，重点在深搜部分，result[num+1]=i; visit[i]=1;  dfs(num+1);  visit[i]=0;这几句很重要，result[num+1]不能写成result[++num]
//因为当回溯时，num的值不能变。