Question

Implement Depth-First Search (DFS) and Breadth-First Search
(BFS) algorithms for a graph in Java.(Can be any graph, just an example of DFS and BFS is sufficient)

If it cannot be done for a graph, then just an example of DFS and BFS are enough.

Answer 1

// Program to print Breadth First Search and Depth First Search for a given grapgh vertex
import java.io.*;
import java.util.*;

// This class represents a graph
class Graph
{
    private int V;   // No. of vertices
    private LinkedList<Integer> adj[]; //Adjacency Lists

    // Constructor to initialize a grapgh
    Graph(int v)
    {
        V = v;
        adj = new LinkedList[v];
        for (int i=0; i<v; ++i)
            adj[i] = new LinkedList();
    }

    // Function to add edge into the graph
    void addEdge(int v,int w)
    {
        adj[v].add(w);
    }

    // Algorith to do breath first search for a provided vertex s
    void BFS(int s)
    {
        // By default mark all vertices as false
        boolean visited[] = new boolean[V];

        // Create a queue for BFS
        LinkedList<Integer> queue = new LinkedList<Integer>();

        // Mark the current node as visited and enqueue it
        visited[s]=true;
        queue.add(s);

        while (queue.size() != 0)
        {
            // Dequeue a vertex from queue and print it
            s = queue.poll();
            System.out.print(s+" ");

            // Get all adjacent vertices of the dequeued vertex s
            // If a adjacent has not been visited, then mark it
            // visited and enqueue it
            Iterator<Integer> i = adj[s].listIterator();
            while (i.hasNext())
            {
                int n = i.next();
                if (!visited[n])
                {
                    visited[n] = true;
                    queue.add(n);
                }
            }
        }
    }
  
   // Function used by depth first search
    void DFSInner(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
        Iterator<Integer> i = adj[v].listIterator();
        while (i.hasNext())
        {
            int n = i.next();
            if (!visited[n])
                DFSInner(n, visited);
        }
    }

    // Algorith to do depth first search for a provided vertex s
    void DFS(int v)
    {
          // By default mark all vertices as false
        boolean visited[] = new boolean[V];

        // Call the recursive helper function to print depth frst search traversal
        DFSInner(v, visited);
    }

    // Invoke the search algorhtms
    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("Breadth First Traversal (starting from vertex 2)");
        g.BFS(2);
      
       System.out.println("------------------------------------------------------------------");
       System.out.println("Depth First Traversal (starting from vertex 2)");
        g.DFS(2);
      
    }
}

Output:
Following is Breadth First Traversal (starting from vertex 2)
2 0 3 1
------------------------------------------------------------------
Following is Depth First Traversal (starting from vertex 2)
2 0 1 3