Java Program to Implement Adjacency List

Code:

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

public class AdjacencyList
{
    private  Map> Adjacency_List;

    public AdjacencyList(int number_of_vertices)
    {
        Adjacency_List = new HashMap>();
        for (int i = 1; i <= number_of_vertices;  i++)
        {
            Adjacency_List.put(i, new LinkedList());
        }
    }

    public void setEdge(int source, int destination)
    {
        if (source > Adjacency_List.size() || destination > Adjacency_List.size())
        {
            System.out.println("the vertex entered in not present ");
            return;
        }
        List slist = Adjacency_List.get(source);
        slist.add(destination);
        List dlist = Adjacency_List.get(destination);
        dlist.add(source);
    }

    public List getEdge(int source)
    {
        if (source > Adjacency_List.size())
        {
            System.out.println("the vertex entered is not present");
            return null;
        }
        return Adjacency_List.get(source);
    }

    public static void main(String...arg)
    {
        int source, destination;
        int number_of_edges, number_of_vertices;
        int count = 1;
        Scanner scan = new Scanner(System.in);
        try
        {
            System.out.println("Enter the number of vertices and edges in graph");
            number_of_vertices = scan.nextInt();
            number_of_edges = scan.nextInt();

            AdjacencyList adjacencyList = new AdjacencyList(number_of_vertices);
            System.out.println("Enter the edges in graph Format : ");
            while (count <= number_of_edges)
            {
                source = scan.nextInt();
                destination = scan.nextInt();
                adjacencyList.setEdge(source, destination);
                count++;
            }
            System.out.println("the given Adjacency List for the graph \n");
            for (int i = 1; i <= number_of_vertices; i++)
            {
                System.out.print(i+"->");
                List edgeList = adjacencyList.getEdge(i);
                for (int j = 1; ; j++ )
                {
                    if (j != edgeList.size())
                        System.out.print(edgeList.get(j - 1 ) + "->");
                    else
                    {
                        System.out.print(edgeList.get(j - 1 ));
                        break;
                    }  
                }
                System.out.println();
            }
        }catch (InputMismatchException inputMismatch)
        {
             System.out.println("Error in Input Format. \nFormat : ");
        }
        scan.close();
    }
}


Output:

Enter the number of vertices and edges in graph
4 5
Enter the edges in graph Format :
1 2
2 3
3 4
4 1
1 3
the given Adjacency List for the graph 

1->2->4->3
2->1->3
3->2->4->1
4->3->1


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