Java Program to Implement Find all Forward Edges in a Graph

This Java program,performs the DFS traversal on the given graph represented by a adjacency matrix to find all the forward edges in a graph.Forward Edges are which point from a node of the tree to one of its descendants.the DFS traversal makes use of an stack.

Here is the source code of the Java program to find the Forward Edges. The Java program is successfully compiled and run on a Linux system. The program output is also shown below.

import java.util.InputMismatchException;
import java.util.Scanner;
import java.util.Stack;
 
public class ForwardEgde
{
    private Stack<Integer> stack;
    private HashMap<Integer, Integer> forwardEdges;
    private int adjacencyMatrix[][];
 
    public ForwardEdge() 
    {
        stack = new Stack<Integer>();
        forwardEdges = new HashMap<Integer, Integer>();
    }
 
    public void dfs(int adjacency_matrix[][], int source)
    {
        int number_of_nodes = adjacency_matrix.length - 1;
        adjacencyMatrix = new int[number_of_nodes + 1][number_of_nodes + 1];
        for (int sourcevertex = 1; sourcevertex <= number_of_nodes; sourcevertex++)
        {
           for (int destinationvertex = 1; destinationvertex <= number_of_nodes; destinationvertex++)
           {
               adjacencyMatrix[sourcevertex][destinationvertex] = 
                    adjacency_matrix[sourcevertex][destinationvertex];
           }
        }
 
        int visited[] = new int[number_of_nodes + 1];		
        int element = source;		
        int destination = source;			
        visited = 1;		
        stack.push(source);
 
        while (!stack.isEmpty())
        {
            element = stack.peek();
            destination = element;	
            while (destination <= number_of_nodes)
	    {
                if (adjacencyMatrix[element][destination] == 1 && visited[destination] == 1)
                {
                    if (!stack.contains(destination))
                    {
                        if (element < destination )	
                            forwardEdges.put(element, destination);	
                    }
                }
                if (adjacencyMatrix[element][destination] == 1 && visited[destination] == 0)
	        {
                    stack.push(destination);
                    visited[destination] = 1;
                    adjacencyMatrix[element][destination] = 0;
                    element = destination;
                    destination = 1;
	            continue;
                }
                destination++;
            }
            stack.pop();	
        } 	
    }
 
    public void printForwardEdges()
    {
        System.out.println("\nSOURCE  : DESTINATION");
        Set<Integer> source = forwardEdges.keySet();
        for (Integer sourcevertex : source)
        {
            System.out.println(sourcevertex + "\t:\t"+ forwardEdges.get(sourcevertex));
        }
    }
 
    public static void main(String...arg)
    {
        int number_of_nodes, source;
        Scanner scanner = null;
 	try
        {
            System.out.println("Enter the number of nodes in the graph");
            scanner = new Scanner(System.in);
            number_of_nodes = scanner.nextInt();
 
	    int adjacency_matrix[][] = new int[number_of_nodes + 1][number_of_nodes + 1];
	    System.out.println("Enter the adjacency matrix");
	    for (int i = 1; i <= number_of_nodes; i++)
	        for (int j = 1; j <= number_of_nodes; j++)
                    adjacency_matrix[i][j] = scanner.nextInt();
 
	    System.out.println("Enter the source for the graph");
            source = scanner.nextInt(); 
 
            ForwardEdge forwardEdge = new ForwardEdge();
            forwardEdge.dfs(adjacency_matrix, source);
            forwardEdge.printForwardEdges();
 
        }catch(InputMismatchException inputMismatch)
        {
            System.out.println("Wrong Input format");
        }	
        scanner.close();	
    }	
}

$javac ForwardEdge.java
$java ForwardEdge
Enter the number of nodes in the graph
4
 
Enter the adjacency matrix
0 1 1 0
0 0 1 0
0 0 0 1
1 0 0 0
 
Enter the source for the graph
1
 
The Forward Edges are
SOURCE  : DESTINATION
1	:	3