class Solution
{
    int[] timeOfInsertion, low;
    boolean[] vis;
    Set<Integer> set;
    int timer;
    public void articulationPoints(int V,ArrayList<ArrayList<Integer>> adj){
        timeOfInsertion = new int[V];
        low = new int[V];
        vis = new boolean[V];
        set = new TreeSet<>();
        timer = 1;
        for(int i=0;i<V;i++){
            if(!vis[i])
                dfs(adj, 0, -1);
        }
        System.out.println(set);
    }
    public void dfs(ArrayList<ArrayList<Integer>> adj, int u, int parent){
        vis[u] = true;
        timeOfInsertion[u] = low[u] = timer++;
        int child = 0;
        for(int v : adj.get(u)){
            if(v == parent) continue;
            if(!vis[v]){
                child++;
                dfs(adj, v, u);
                low[u] = Math.min(low[u], low[v]);
                if(low[v] >= timeOfInsertion[u] && parent != -1)
                    set.add(u);
            }else low[u] = Math.min(low[u], timeOfInsertion[v]);
        }
        if(parent == -1 && child > 1) 
            set.add(u);
    }
}