lessons/参考实现/01-欧拉路径/POJ-2230.cpp

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, m;
    cin >> n >> m;
    vector<vector<int>> adj(n + 1);
    for (int i = 0; i < m; ++i) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);  // 独立的反向弧，不与上一条共享 used 标记
    }

    vector<size_t> cursor(n + 1, 0);
    vector<int> st{1}, path;
    path.reserve(2 * m + 1);
    while (!st.empty()) {
        int v = st.back();
        if (cursor[v] == adj[v].size()) {
            path.push_back(v);
            st.pop_back();
        } else {
            st.push_back(adj[v][cursor[v]++]);
        }
    }
    reverse(path.begin(), path.end());
    for (int v : path) cout << v << '\n';
}