poj2230 Watchcow（欧拉回路）

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <vector>
#include <stack>
#define rep(x, l, r) for(int x = l; x <= r; x++)
#define repd(x, r, l) for(int x = r; x >= l; x--)
#define clr(x, y) memset(x, y, sizeof(x))
#define all(x) x.begin(), x.end()
#define pb push_back
#define mp make_pair
#define MAXN 100005
#define MAXM 1000005
#define fi first
#define se second
#define SZ(x) ((int)x.size())
using namespace std;
typedef long long LL;
typedef vector<int> vi;
typedef pair<int, int> pii;
const int INF = 0x3f3f3f3f;
const int p = 10000007;
int lowbit(int x){ return x & -x; }
int fast_power(int a, int b){ int x; for(x = 1; b; b >>= 1){ if(b & 1) x = 1ll * x * a % p; a = 1ll * a * a % p; } return x; }

stack<int> sta;
int n, cnt, tot;
int head[MAXN], nxt[MAXM], to[MAXM];
int ans[2 * MAXN];
bool vis[MAXM];

void init(){
    cnt = 0;
    clr(head, -1);
}

void add(int u, int v){
    nxt[cnt] = head[u];
    head[u] = cnt;
    to[cnt] = v;
    cnt++;
}

void euler(){
    sta.push(1);
    while(!sta.empty()){
        int u = sta.top(), e = head[u];
        while(e != -1&& vis[e]) e = nxt[e];
        if(e != -1){
            int v = to[e];
            sta.push(v);
            vis[e] = 1;
            head[u] = nxt[e];
        }
        else{
            sta.pop();
            ans[++tot] = u;
        }
    }
}

int main(){
    init();
    int m;
    scanf("%d%d", &n, &m);
    rep(i, 1, m){
        int u, v;
        scanf("%d%d", &u, &v);
        add(u, v), add(v, u);
    }
    euler();
    repd(i, tot, 1) printf("%d\n", ans[i]);
    return 0;
}