Method find

Data Structures/Reachability Tree.cpp:10–13

reachability tree

  int T, st[2 * N], en[2 * N];
  vector<int> g[2 * N]; //reachability tree
  int find(int x) {
    if (par[x] == x) return x;
    return par[x] = find(par[x]);
  }
  void dfs(int u) {
    st[u] = T + 1;
    for (int v : g[u]) {