典型的找欧拉路径的题。先贴下USACO上找欧拉路径的法子：
- Pick a starting node and recurse on that node. At each step:
- If the node has no neighbors, then append the node to the circuit and return
- If the node has a neighbor, then make a list of the neighbors and process them (which includes deleting them from the list of nodes on which to work) until the node has no more neighbors
- To process a node, delete the edge between the current node and its neighbor, recurse on the neighbor, and postpend the current node to the circuit。
但实际写的时候其实用DFS起来更加方便。这道题我一开始用stack，但是始终不能找到输出的序列在500位制情况下最小的解，于是从网上看到有人用dfs轻松简单方便地就解决了。。。
/*
ID: yingzho1
LANG: C++
TASK: fence
*/
#include <iostream>
#include <fstream>
#include <string>
#include <map>
#include <vector>
#include <set>
#include <algorithm>
#include <stdio.h>
#include <queue>
#include <cstring>
#include <cmath>
#include <list>
#include <cstdio>
#include <cstdlib>
#include <limits>
#include <stack>
using namespace std;
ifstream fin("fence.in");
ofstream fout("fence.out");
;
};
];
int F, st, ans_tot;
void dfs(int st) {
; i < MAX; i++) {
if (edge[st][i]) {
edge[st][i]--, edge[i][st]--;
du[st]--, du[i]--;
dfs(i);
}
}
ans[++ans_tot] = st;
}
int main()
{
fin >> F;
int x, y;
; i < F; i++) {
fin >> x >> y;
edge[x][y]++, edge[y][x]++;
du[x]++, du[y]++;
}
st = ;
; i < MAX; i++) {
) {
st = i;
break;
}
}
) {
; i < MAX; i++) {
if (du[i]) {
st = i;
break;
}
}
}
dfs(st);
; i--) fout << ans[i] << endl;
;
}