void solve() {
    int n, m; // 点和边数量
    vector e(n + 1, vector<pii>()); // pii 存 出点 边标号
    vector<int> visi(m + 1);
    vector<int> path;
    auto dfs = [&] (auto &&self, int u)->void {
        for (auto [v, id] : u) {
            if (!visi[id]) {
                visi[id] = 1;
                self(self, v);
            }
        }
        path.push_back(u);
    };
    reverse(path.begin(), path.end());
}