Java Program to Describe the Representation of Graph using Incidence List

Code:

import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Scanner;

public class IncidentList
{
    private Map> incidentList;
    private int numberOfVertices;

    public IncidentList(int numberOfVertices)
    {
        this.numberOfVertices = numberOfVertices;
        incidentList = new HashMap>();

        for (int vertex = 1; vertex <= numberOfVertices; vertex++)
            incidentList.put(vertex, new LinkedList());
    }

    public void setEdge(int sourcevertex, int destinationvertex, int edgeNumber)
    {
        List slist = incidentList.get(sourcevertex);
        slist.add(edgeNumber);
        return;
    }

    public List getEdge(int vertex)
    {
        return incidentList.get(vertex);
    }

    public void printIncidentList()
    {
        System.out.println("Vertex   EdgeNumber");
        for (int vertex = 1; vertex <= numberOfVertices; vertex++)
        {
            System.out.print(vertex + ":");
            List edgeList = getEdge(vertex);

            for (int j = 1; ; j++)
            {
                if (j != edgeList.size())
                    System.out.print(edgeList.get(j - 1) + "\t");
                else
                {
                    System.out.print(edgeList.get(j - 1));
                    break;
                }
            }
            System.out.println();
        }
    }

    public static void main(String... arg)
    {
        int numberOfVertices, numberOfEdges;
        int source, destination, edgeNumber;
        int edgeCount = 1;

        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the number of vertices");
        numberOfVertices = scanner.nextInt();

        IncidentList incidentList = new IncidentList(numberOfVertices);
        System.out.println("Enter the number of edges");
        numberOfEdges = scanner.nextInt();

        System.out.println("Enter the edges format : ");
        while (edgeCount <= numberOfEdges)
        {
            edgeNumber = scanner.nextInt();
            source = scanner.nextInt();
            destination = scanner.nextInt();
            incidentList.setEdge(source, destination, edgeNumber);
            edgeCount++;
        }

        System.out.println("\nThe Incident List is ");
        incidentList.printIncidentList();
        scanner.close();
    }
}


Output:

Enter the number of vertices
5
Enter the number of edges
5
Enter the edges format :
1 1 2
2 2 4 
3 5 4
4 4 3
5 5 1

The Incident List is 
Vertex   EdgeNumber
  1    : 1 5
  2    : 1 2
  3    : 4
  4    : 2 3 4
  5    : 3 5


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