题目

DFS直接就可以解决，就是样例的输出有点吓人。

#include<iostream>
#include<cstdio>  
#include<cstring>  
#include<algorithm>  
using namespace std;  
  
int map[21][4];  
int vis[21];  
int ans[21];  
int icase=1;  
int n,m;  
  
void dfs(int m,int len,int c)  
{  
    int i,j;  
    vis[m] = 1;  
    ans[len] = m;  
    for(i = 0; i<3; i++)  
    {  
        int t = map[m][i];  
        if(t == c && len == 19)  
        {  
            printf("%d:  ",icase++);  
            for(j=0;j<20;j++)  
                printf("%d ",ans[j]);  
            printf("%d\n",c);  
        }  
        if(!vis[t])  
            dfs(t,len+1,c);  
    }  
    vis[m] = 0;  
}  
  
int main()  
{  
    int i;  
    for(i = 1; i<=20; i++)  
        scanf("%d%d%d",&map[i][0],&map[i][1],&map[i][2]);  
    while(~scanf("%d",&m),m)  
    {  
        memset(vis,0,sizeof(vis));  
        dfs(m,0,m);  
    }  
  
    return 0;  
}