題目連結：https://vjudge.net/problem/HDU-2181#author=0

思路：簡單搜尋，直接dfs即可

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int a[30][30],b[30];
int book[30];
int v=0;
void dfs(int x,int y,int m)
{
    if(y==21)
    {
        if(a[x][m]==1)
        {
            printf("%d:  ",++v);
            
 
for(int i=1;i<=20;i++)
                cout<<b[i]<<" ";
            cout<<m<<endl;
        }
        return;
    }
    for(int i=1;i<=20;i++)
    {
        if(book[i]==1||a[x][i]==0)
            continue;
        book[i]=1;
        b[y]=i;
        dfs(i,y+1,m);
        book[i]
 
=0;
    }
}
int main()
{
    for(int i=1;i<=20;i++)
    {
        int x,y,z;
        cin>>x>>y>>z;
        a[i][x]=a[i][y]=a[i][z]=1;
    }
    int m;
    while(~scanf("%d",&m))
    {
        memset(book,0,sizeof(book));
        if(m==0)
            break;
        v=0;
        book[m]
 
=1;
        b[1]=m;
        dfs(m,2,m);
    }
}