HDU 1016 Prime Ring Problem（DFS）

HDU 1016 Prime Ring Problem
题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1016
dfs进行遍历即可

#include<cstdio>
#include<iostream>
#include<cstring> 
using namespace std;
//n最大为20，打表到40即可 
int prime[40]={0,1,1,1,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,1,0,0,0,1,0,0,0,0,0,1,0,1,0,0,0,0,0,1,0,0}; 
int vis[21],a[21];
int n;

void dfs(int num){
    int i;
    if(num==n&&prime[a[0]+a[num-1]]){       //满足题意则输出 
        for(i=0;i<num-1;i++)
            printf("%d ",a[i]);
        printf("%d\n",a[num-1]);
    }
    else{
        for(i=2;i<=n;i++){          //否则从第二位起开始判断 
            if(vis[i]==0&&prime[i+a[num-1]]){       //没用过且与邻位加和为素数 
                vis[i]=1;
                a[num++]=i;         //加入 
                dfs(num);
                vis[i]=0;           //清除标记 
                num--;              
            }
        }
    }
}

int main(){
    int num=0;
    while(scanf("%d",&n)!=EOF){
        num++;
        printf("Case %d:\n",num);
        memset(vis,0,sizeof(vis));
        a[0]=1;
        dfs(1);
        printf("\n");
    }
    return 0;
} 

参考：https://www.cnblogs.com/jiangjing/archive/2013/02/04/2891621.html