Java Program to Implement Find all Back Edges in a Graph

This Java program,performs the DFS traversal on the given graph represented by a adjacency matrix to find all the back edges in a graph.the DFS traversal makes use of an stack.

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

import java.util.HashMap;
import java.util.InputMismatchException;
import java.util.Scanner;
import java.util.Set;
import java.util.Stack;
 
public class BackEdges
{
    private Stack<Integer> stack;
    private HashMap<Integer, Integer> backEdges;
    private int adjacencyMatrix[][];
 
    public BackEdges() 
    {
        stack = new Stack<Integer>();
        backEdges = 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))
                    {	
                        backEdges.put(element, destination);
                        adjacencyMatrix[element][destination]= 0;	
                    }
                }
 
     	        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 printBackEdges()
    {
        System.out.println("\nSOURCE  : DESTINATION");
        Set<Integer> source = backEdges.keySet();
        for (Integer sourcevertex : source)
        {
            System.out.println(sourcevertex + "\t:\t"+ backEdges.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(); 
 
            BackEdges backEdges = new BackEdges();
            backEdges.dfs(adjacency_matrix, source);
            backEdges.printBackEdges();
 
        }catch(InputMismatchException inputMismatch)
        {
            System.out.println("Wrong Input format");
        }	
        scanner.close();	
    }	
}

$javac BackEdges.java
$java BackEdges
Enter the number of nodes in the graph
4
Enter the adjacency matrix
0 1 0 0 
0 0 1 0
0 0 0 1
0 1 0 0 
Enter the source for the graph
1
The Back Edges are given by
 
SOURCE  : DESTINATION
4	:	2