#define PROBLEM "https://yukicoder.me/problems/no/2780" #include struct SCC { int n, group_num; std::vector> &g; std::vector ids; SCC(std::vector> &_g) : n(_g.size()), g(_g), ids(n), group_num(0) { int now_ord = 0; std::vector visited, low(n), ord(n, -1); visited.reserve(n); auto dfs = [&](auto self, int v) -> void { low[v] = ord[v] = now_ord++; visited.emplace_back(v); for(auto to : g[v]) { if (ord[to] == -1) { self(self, to); low[v] = std::min(low[v], low[to]); } else { low[v] = std::min(low[v], ord[to]); } } if (low[v] == ord[v]) { while (true) { int u = visited.back(); visited.pop_back(); ord[u] = n; ids[u] = group_num; if (u == v) break; } group_num++; } }; for (int i = 0; i < n; i++) { if (ord[i] == -1) dfs(dfs, i); } for (auto& x : ids) { x = group_num - 1 - x; } } const int operator[](int p) const { assert(0 <= p && p < n); return ids[p]; } int operator[](int p) { assert(0 <= p && p < n); return ids[p]; } std::vector> groups(){ std::vector counts(group_num); for (auto x : ids) counts[x]++; std::vector> groups(group_num); for (int i = 0; i < group_num; i++) { groups[i].reserve(counts[i]); } for (int i = 0; i < n; i++) { groups[ids[i]].emplace_back(i); } return groups; } }; using namespace std; int main(){ ios::sync_with_stdio(false); cin.tie(0); int n; cin >> n; vector> g(n); for(int i = 0; i < n; i++){ int m; cin >> m; g[i].resize(m); for(auto &&v : g[i]){ cin >> v; v--; } } SCC scc(g); auto G = scc.groups(); if(find(G[0].begin(), G[0].end(), 0) == G[0].end()){ cout << "No\n"; return 0; } vector dp(G.size()); for(int i = 0; i < G.size(); i++){ const int id = scc[G[i][0]]; if(dp[id] != i){ cout << "No\n"; return 0; } for(auto &&v : G[i]){ for(auto &&u : g[v]){ if(scc[u] == id) continue; dp[scc[u]] = max(dp[scc[u]], dp[id] + 1); } } } cout << "Yes\n"; }