CyclicGraph.java

/*
    Name: Is Graph Cyclic
    Source: PepCoding
    Link: https://www.pepcoding.com/resources/online-java-foundation/graphs/is-cyclic-official/ojquestion
    Statement: You are required to find and print if the graph is cyclic.
 */

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

public class CyclicGraph {
    static class Edge {
        int src;
        int nbr;
        int wt;

        Edge(int src, int nbr, int wt) {
            this.src = src;
            this.nbr = nbr;
            this.wt = wt;
        }
    }

    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        int vtces = Integer.parseInt(br.readLine());
        ArrayList < Edge > [] graph = new ArrayList[vtces];
        for (int i = 0; i < vtces; i++) {
            graph[i] = new ArrayList < > ();
        }

        int edges = Integer.parseInt(br.readLine());
        for (int i = 0; i < edges; i++) {
            String[] parts = br.readLine().split(" ");
            int v1 = Integer.parseInt(parts[0]);
            int v2 = Integer.parseInt(parts[1]);
            int wt = Integer.parseInt(parts[2]);
            graph[v1].add(new Edge(v1, v2, wt));
            graph[v2].add(new Edge(v2, v1, wt));
        }

        boolean check = false;
        boolean [] visited = new boolean[vtces];
        for(int i=0; i<vtces; i++)
        {
            if(!visited[i])
            {
                check = isCyclic(i, visited, graph);
                if(check)
                {
                    break;
                }
            }
        }

        System.out.println(check);
    }

    public static boolean isCyclic(int src, boolean [] visited, ArrayList < Edge > [] graph)
    {
        ArrayDeque<Integer> que = new ArrayDeque<>();
        que.add(src);

        while(que.size()>0)
        {
            int top = que.remove();
            if(visited[top])
            {
                return true;
            }

            visited[top] = true;

            for(Edge edge: graph[top] )
            {
                if(!visited[edge.nbr])
                {
                    que.add(edge.nbr);
                }
            }
        }

        return false;
    }
}