#line 1 "main.cpp" #include <bits/stdc++.h> #define rep(i, n) for (int i = 0; i < (int)(n); i++) #define rrep(i, n) for (int i = (int)(n - 1); i >= 0; i--) #define all(x) (x).begin(), (x).end() #define sz(x) int(x.size()) using namespace std; using ll = long long; constexpr int INF = 1e9; constexpr ll LINF = 1e18; string YesNo(bool cond) { return cond ? "Yes" : "No"; } string YESNO(bool cond) { return cond ? "YES" : "NO"; } template <class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } return false; } template <class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } return false; } template <typename T, class F> T bisect(T ok, T ng, const F& f) { while (abs(ok - ng) > 1) { T mid = min(ok, ng) + (abs(ok - ng) >> 1); (f(mid) ? ok : ng) = mid; } return ok; } template <typename T, class F> T bisect_double(T ok, T ng, const F& f, int iter = 100) { while (iter--) { T mid = (ok + ng) / 2; (f(mid) ? ok : ng) = mid; } return ok; } template <class T> vector<T> make_vec(size_t a) { return vector<T>(a); } template <class T, class... Ts> auto make_vec(size_t a, Ts... ts) { return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...)); } template <typename T> istream& operator>>(istream& is, vector<T>& v) { for (int i = 0; i < int(v.size()); i++) { is >> v[i]; } return is; } template <typename T> ostream& operator<<(ostream& os, const vector<T>& v) { for (int i = 0; i < int(v.size()); i++) { os << v[i]; if (i < sz(v) - 1) os << ' '; } return os; } #line 2 "/Users/gyouzasushi/kyopro/library/graph/functional_graph.hpp" #line 5 "/Users/gyouzasushi/kyopro/library/graph/functional_graph.hpp" struct functional_graph { public: functional_graph(int n) : _n(n), graph(n) { } void add_edge(int u, int v) { graph[u].push_back(v); graph[v].push_back(u); } void add_directed_edge(int from, int to) { graph[from].push_back(to); } std::vector<int> loop() { std::vector<int> path; std::vector<int> check(_n, 0); auto dfs = [&](auto dfs, int u, int p) -> int { check[u]++; path.push_back(u); for (int v : graph[u]) { if (v == p) continue; if (check[v] == 0) { int ret = dfs(dfs, v, u); if (ret != -1) return ret; } else if (check[v] == 1) { return v; } } path.pop_back(); check[u]++; return -1; }; std::vector<int>::iterator it = std::find(path.begin(), path.end(), dfs(dfs, 0, -1)); return std::vector(it, path.end()); } std::vector<std::vector<std::vector<int>>> tree() { return {}; } private: int _n; std::vector<std::vector<int>> graph; }; #line 73 "main.cpp" int main() { int n; cin >> n; functional_graph g(n); map<pair<int, int>, int> id; rep(i, n) { int a, b; cin >> a >> b; g.add_edge(--a, --b); id[{a, b}] = id[{b, a}] = i; } vector loop = g.loop(); int k = sz(loop); cout << k << '\n'; rep(i, k) { int u = loop[i]; int v = loop[(i + 1) % k]; cout << id[{u, v}] + 1 << " \n"[i == k - 1]; } }