Bridges + Articulation Points (Tarjan's)

int[] disc, low;
int time = 0;
Set bridges = new HashSet<>();
Set articulations = new HashSet<>();
void dfs(int u, int parent) {
  disc[u] = low[u] = time++;
  int children = 0;
  for (int v : graph[u]) {
    if (v == parent) continue;
    if (disc[v] == -1) {
      children++;
      dfs(v, u);
      low[u] = min(low[u], low[v]);
      if (low[v] > disc[u]) bridges.add(new int[]{u, v});
      if (parent != -1 && low[v] >= disc[u]) articulations.add(u);
    } else {
      low[u] = min(low[u], disc[v]);
    }
  }
  if (parent == -1 && children > 1) articulations.add(u);
}