CycleDetectedGraph.java

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

class Node{
    int first;
    int second;
    public Node(int first, int second){
        this.first = first;
        this.second = second;
    }
}

class Solution{
    static boolean checkForCycle(ArrayList<ArrayList<Integer>> adj, int s, boolean vis[]){
        Queue<Node>q =new LinkedList<>(); //Bfs
        q.add(new Node(s,-1));
        vis[s]=true;

        while(!q.isEmpty())
        {
            int node=q.peek().first;
            int par=q.peek().second;
            q.remove();

            for(Integer it:adj.get(node))
            {
                if(vis[it]==false)
                {
                    q.add(new Node(it,node));
                    vis[it]=true;
                }

                else if(par != it) return true;
            }
        }
        return false;
    }

    public boolean isCycle(int V, ArrayList<ArrayList<Integer>> adj)
    {
        boolean vis[]=new boolean[V+1];
        Arrays.fill(vis,false); //initialize all to false   
        for(int i=0;i<V;i++)
        {
            if(vis[i]==false)
            {
                if(checkForCycle(adj,i,vis))
                 return true;
            }
        }
        return false;
    }
}