Articulation Point - II

import java.util.*;

class Solution {
    static ArrayList<Integer> articulationPoints(int V, int[][] edges) {
        ArrayList<ArrayList<Integer>> adj = new ArrayList<>();

        for (int i = 0; i < V; i++)
            adj.add(new ArrayList<>());

        for (int[] edge : edges) {
            adj.get(edge[0]).add(edge[1]);
            adj.get(edge[1]).add(edge[0]);
        }

        int[] tin = new int[V];
        int[] low = new int[V];
        boolean[] vis = new boolean[V];
        boolean[] isArticulation = new boolean[V];
        int[] timer = { 0 };

        for (int i = 0; i < V; i++) {
            if (!vis[i])
                dfs(i, -1, adj, vis, tin, low, timer, isArticulation);
        }

        ArrayList<Integer> ans = new ArrayList<>();
        for (int i = 0; i < V; i++) {
            if (isArticulation[i])
                ans.add(i);
        }

        if (ans.size() == 0)
            ans.add(-1);

        return ans;
    }

    static void dfs(int u, int parent, ArrayList<ArrayList<Integer>> adj, boolean[] vis, int[] tin, int[] low,
            int[] timer, boolean[] isArticulation) {
        vis[u] = true;
        tin[u] = low[u] = timer[0]++;
        int children = 0;

        for (int v : adj.get(u)) {

            if (v == parent)
                continue;

            if (!vis[v]) {
                dfs(v, u, adj, vis, tin, low, timer, isArticulation);
                low[u] = Math.min(low[u], low[v]);
                if (low[v] >= tin[u] && parent != -1)
                    isArticulation[u] = true;

                children++;
            } else
                low[u] = Math.min(low[u], tin[v]);
        }
        if (parent == -1 && children > 1)
            isArticulation[u] = true;
    }
}