Articulation Point

import java.io.*;
import java.util.*;
import java.util.LinkedList;

class Graph
{
    private int V;
    private LinkedList<Integer> adj[];
    int time = 0;
    static final int NIL = -1;


    Graph(int v)
    {
        V = v;
        adj = new LinkedList[v];
        for (int i=0; i<v; ++i)
        {
            adj[i] = new LinkedList();
        }
    }


    void addEdge(int v, int w)
    {
        adj[v].add(w);
        adj[w].add(v);
    }


    void APCheck(int u, boolean visited[], int discover[], int low[], int parent[], boolean ap[])
    {
        int children = 0;
        visited[u] = true;
        discover[u] = low[u] = ++time;
        Iterator<Integer> i = adj[u].iterator();
        while (i.hasNext())
        {
            int v = i.next();
            if (!visited[v])
            {
                children++;
                parent[v] = u;
                APCheck(v, visited, discover, low, parent, ap);

                low[u]  = Math.min(low[u], low[v]);

                if (parent[u] == NIL && children > 1)
                {
                    ap[u] = true;
                    //System.out.println(u);
                }

                if (parent[u] != NIL && low[v] >= discover[u])
                {
                    ap[u] = true;
                    //System.out.println(u);
                }
            }


            else if (v != parent[u])
            {
                low[u]  = Math.min(low[u], discover[v]);
            }
        }
    }


    void AP()
    {

        boolean visited[] = new boolean[V];
        int discover[] = new int[V];
        int low[] = new int[V];
        int parent[] = new int[V];
        boolean ap[] = new boolean[V];


        for (int i = 0; i < V; i++)
        {
            parent[i] = NIL;
            visited[i] = false;
            ap[i] = false;
        }


        for (int i = 0; i < V; i++)
        {
            if (visited[i] == false)
            {
                APCheck(i, visited, discover, low, parent, ap);
            }
        }


        for (int i = 0; i < V; i++)
        {
            if (ap[i] == true)
            {
                System.out.print(i+" ");
            }
        }

    }

    // Driver method
    public static void main(String args[])
    {
        System.out.println("Articulation points in Given graph");
        Graph g4 = new Graph(6);
        g4.addEdge(0,3);
        g4.addEdge(0,2);
        g4.addEdge(3,5);
        g4.addEdge(3,1);
        g4.addEdge(2,4);
        g4.AP();

    }
}