POJ – 2230 Watchcow(欧拉回路变形)

#include<algorithm>
#include <iostream>
#include  <fstream>
#include  <cstdlib>
#include  <cstring>
#include  <cassert>
#include   <cstdio>
#include   <vector>
#include   <string>
#include    <cmath>
#include    <queue>
#include    <stack>
#include      <set>
#include      <map>
using namespace std;
#define P(a,b,c) make_pair(a,make_pair(b,c))
#define rep(i,a,n) for (int i=a;i<=n;i++)
#define per(i,a,n) for (int i=n;i>=a;i--)
#define CLR(vis) memset(vis,0,sizeof(vis))
#define MST(vis,pos) memset(vis,pos,sizeof(vis))
#define pb push_back
//#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef pair<int,pair<int,int> >pii;
typedef long long ll;
typedef unsigned long long ull;
const ll mod = 1000000007;
const int INF = 0x3f3f3f3f;
ll gcd(ll a, ll b) {
	return b ? gcd(b, a%b) : a;
}
template<class T>inline void gmax(T &A, T B) {
	(A<B)&&(A=B);//if(B>A)A=B;
}
template<class T>inline void gmin(T &A, T B) {
	(A>B)&&(A=B);//if(B<A)A=B;
}
template <class T>
inline bool scan(T &ret) {
	char c;
	int sgn;
	if(c=getchar(),c==EOF) return 0; //EOF
	while(c!='-'&&(c<'0'||c>'9')) c=getchar();
	sgn=(c=='-')?-1:1;
	ret=(c=='-')?0:(c-'0');
	while(c=getchar(),c>='0'&&c<='9') ret=ret*10+(c-'0');
	ret*=sgn;
	return 1;
}
inline void outt(int x) {
	if(x>9) outt(x/10);
	putchar(x%10+'0');
}
const int N = 100010,M = 1000010;
int head[N], ver[M], Next[M], tot;
int STA[M], ans[M];
int n,m,top,t;


void add(int x,int y){
	ver[++tot] = y;
	Next[tot] = head[x];
	head[x] = tot;
}


void euler(){
	STA[++top] = 1;
	while(top>0){
		int x = STA[top], i = head[x];
		if(i){
			STA[++top] = ver[i];
			head[x] = Next[i];
		}else{
			--top;
			ans[++t] = x;
		}
	}
}

int main(){
	cin>>n>>m;
	tot = 1;
	top = 0;
	memset(head, 0 ,sizeof(head));
	rep(i,1,m){
		int x,y;
		scanf("%d%d", &x, &y);
		add(x,y), add(y,x); 
	}
	euler();
	per(i,1,t){
		printf("%d\n", ans[i]);
	}
	return 0; 
}