Lab7q7.java

import java.util.*;

public class Lab7q7 {
    public static void main(String[] args) {
        ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
        int vertices = 4;

        for (int i = 0; i < vertices; i++) {
            graph.add(new ArrayList<>());
        }

        graph.get(0).add(1);
        graph.get(0).add(2);
        graph.get(1).add(3);
//        graph.get(2).add(1);
        graph.get(3).add(2);

        boolean hasCycle = isCyclicBFS(graph, vertices);

        if (hasCycle) {
            System.out.println("The graph contains a cycle.");
        } else {
            System.out.println("The graph does not contain a cycle.");
        }
    }

    static boolean isCyclicBFS(ArrayList<ArrayList<Integer>> graph, int vertices) {
        int[] inDegree = new int[vertices];
        for (int i = 0; i < vertices; i++) {
            for (int neighbor : graph.get(i)) {
                inDegree[neighbor]++;
            }
        }

        Queue<Integer> queue = new LinkedList<>();
        for (int i = 0; i < vertices; i++) {
            if (inDegree[i] == 0) {
                queue.add(i);
            }
        }

        int count = 0;
        while (!queue.isEmpty()) {
            int current = queue.poll();
            count++;

            for (int neighbor : graph.get(current)) {
                inDegree[neighbor]--;

                if (inDegree[neighbor] == 0) {
                    queue.add(neighbor);
                }
            }
        }

        return count != vertices;
    }
}