// Import necessary packages
import java.util.*;

/**
 * This class represents a graph using adjacency list representation
 */
class Graph {
    // Number of vertices in the graph
    private int V;

    // Array of lists for adjacency list representation
    private LinkedList<Integer> adj[];

    /**
     * Constructor to initialize the graph
     * 
     * @param v Number of vertices
     */
    Graph(int v) {
        V = v;
        adj = new LinkedList[v];
        for (int i = 0; i < v; ++i)
            adj[i] = new LinkedList();
    }

    /**
     * Function to add an edge into the graph
     * 
     * @param v Source vertex
     * @param w Destination vertex
     */
    void addEdge(int v, int w) {
        adj[v].add(w);
    }

    /**
     * A function used by DFS
     * 
     * @param v The starting vertex
     * @param visited Array to keep track of visited vertices
     */
    void DFSUtil(int v, boolean visited[]) {
        // Mark the current node as visited and print it
        visited[v] = true;
        System.out.print(v + " ");

        // Recur for all the vertices adjacent to this vertex
        for (Integer n : adj[v]) {
            if (!visited[n])
                DFSUtil(n, visited);
        }
    }

    /**
     * The function to do DFS traversal. It uses DFSUtil()
     * 
     * @param v The starting vertex
     */
    void DFS(int v) {
        // Mark all the vertices as not visited (set as false by default in Java)
        boolean visited[] = new boolean[V];

        // Call the recursive helper function to print DFS traversal</span
        DFSUtil(v, visited);
    }

    /**
     * Main method to test the DFS algorithm
     */
    public static void main(String args[]) {
        Graph g = new Graph(4);

        g.addEdge(0, 1);
        g.addEdge(0, 2);
        g.addEdge(1, 2);
        g.addEdge(2, 0);
        g.addEdge(2, 3);
        g.addEdge(3, 3);

        System.out.println("Following is Depth First Traversal (starting from vertex 2)");

        g.DFS(2);
    }
}