_152cycle.java

import java.util.*;
public class _152cycle {
    static class Edge{
        int src;
        int dest;
        public Edge(int s, int d){
            this.src=s;
            this.dest=d;
        }
    }
    static void createGraph(ArrayList<Edge>[] graph){
        for(int i=0;i<graph.length;i++){
            graph[i]=new ArrayList<>();
        }
        graph[0].add(new Edge(0,1));
        graph[0].add(new Edge(0,2));

        graph[1].add(new Edge(1,0));
        graph[1].add(new Edge(1,3));
        
        graph[2].add(new Edge(2,3));
        graph[2].add(new Edge(2,3));
        
        graph[3].add(new Edge(3,1));
        graph[3].add(new Edge(3,4));
        graph[3].add(new Edge(3,5));
        
        graph[4].add(new Edge(4,2));
        graph[4].add(new Edge(4,3));
        graph[4].add(new Edge(4,5));
        
        graph[5].add(new Edge(5,3));
        graph[5].add(new Edge(5,4));
        graph[5].add(new Edge(5,6));
        
        graph[6].add(new Edge(6,5));

    }
    public static boolean detectCycle(ArrayList<Edge>[] graph){
        boolean vis[]=new boolean[graph.length];
        for(int i=0;i<graph.length;i++){
            if(!vis[i]){
                if(detectCycleUtil(graph,vis,i,-1)){
                    return true;
                }
            }
        }
        return false;
    }
    public static boolean detectCycleUtil(ArrayList<Edge>[] graph,boolean vis[],int curr, int par){
        vis[curr]=true;
        for(int i=0;i<graph[curr].size();i++){
            Edge e = graph[curr].get(i);
            if(!vis[e.dest]){
                if(detectCycleUtil(graph,vis,e.dest,curr)){
                    return true;
                }
            } else if(vis[e.dest] && e.dest != par){
                return true;
            }
        }
        return false;
    }
    public static void main(String[] args) {
        int V=7;
        @SuppressWarnings("unchecked")
        ArrayList<Edge> graph[] = new ArrayList[V];
        createGraph(graph);
        System.out.println(detectCycle(graph));
    }
}