poj2230 Watchcow(欧拉回路:输出点轨迹)

题意：有一个有向图，输出从1点出发经过所有边再回到1的路径，保证这种路径存在

思路：其实就要输出有向图的欧拉回路，其中把每一条边都正向反向添加进图，然后递归输出即可

#include <cstdio>
#include <queue>
#include <cstring>
#include <iostream>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <map>
#include <string>
#include <set>
#include <ctime>
#include <cmath>
#include <cctype>
using namespace std;
#define maxn 50000+10
#define maxm 10000+10
#define LL long long
int cas=1,T;
int n,m;
struct Edge
{
int v;
bool vis;
Edge(){}
Edge(int v,bool vis):v(v),vis(vis){}
}edges[maxm*2];
vector<Edge>G[maxn];
void init()
{
for (int i = 0;i<=n;i++)
G[i].clear();
}
void euler(int u)
{
for (int i = 0;i<G[u].size();i++)
{
Edge &e = G[u][i];
if (!e.vis)
{
e.vis=1;
euler(e.v);
}
}
printf("%d\n",u);
}
int main()
{
scanf("%d%d",&n,&m);
for (int i = 1;i<=m;i++)
{
int u,v;
scanf("%d%d",&u,&v);
G[u].push_back(Edge(v,false));
G[v].push_back(Edge(u,false));
}
euler(1);
//freopen("in","r",stdin);
//scanf("%d",&T);
//printf("time=%.3lf",(double)clock()/CLOCKS_PER_SEC);
return 0;
}

Description

Bessie's been appointed the new watch-cow for the farm. Every night, it's her job to walk across the farm and make sure that no evildoers are doing any evil. She begins at the barn, makes her patrol, and then returns to the barn when she's done.

If she were a more observant cow, she might be able to just walk each of M (1 <= M <= 50,000) bidirectional trails numbered 1..M between N (2 <= N <= 10,000) fields numbered 1..N on the farm once and be confident that she's seen everything she needs to see.
But since she isn't, she wants to make sure she walks down each trail exactly twice. It's also important that her two trips along each trail be in opposite directions, so that she doesn't miss the same thing twice.

A pair of fields might be connected by more than one trail. Find a path that Bessie can follow which will meet her requirements. Such a path is guaranteed to exist.

Input

* Line 1: Two integers, N and M.

* Lines 2..M+1: Two integers denoting a pair of fields connected by a path.

Output

* Lines 1..2M+1: A list of fields she passes through, one per line, beginning and ending with the barn at field 1. If more than one solution is possible, output any solution.

Sample Input

4 5
1 2
1 4
2 3
2 4
3 4

Sample Output

1
2
3
4
2
1
4
3
2
4
1

Hint

OUTPUT DETAILS:

Bessie starts at 1 (barn), goes to 2, then 3, etc...