HDU 2181 哈密顿绕行世界问题 （DFS）

#include <bits/stdc++.h>
using namespace std;

int city[30][5];
int vis[30];
int pre[30];
int m;
int cnt;

void print_ans(int cur){
    if(cur != m){
        print_ans(pre[cur]);
        printf(" %d", cur);
    }
}

void dfs(int now, int step){
    if(step < 20 && vis[m]) return ;
    if(now == m && step == 20){
        printf("%d:  %d", ++cnt, m);
        print_ans(pre[m]);
        printf(" %d\n", m);
        return ;
    }
    for(int i=0; i<3; i++){
        int tp = city[now][i];
        if(!vis[tp]){
            vis[tp] = true;
            pre[tp] = now;
            dfs(tp, step+1);
            vis[tp] = false;        //搜完要恢复标记。。。
        }
    }
}

int main(){
    #ifdef sxk
        freopen("in.txt", "r", stdin);
    #endif //sxk

    int a, b, c;
    for(int i=1; i<=20; i++){
        scanf("%d%d%d", &a, &b, &c);
        if(b > c) swap(b, c);        //手动排序
        if(a > b) swap(a, b);
        if(b > c) swap(b, c);
        city[i][0] = a, city[i][1] = b, city[i][2] = c;
    }
    while(scanf("%d", &m) == 1 && m){
        memset(vis, false, sizeof(vis));
        memset(pre, 0, sizeof(pre));
        cnt = 0;
        dfs(m, 0);
    }
    return 0;
}