Skip to content
Related Articles

Related Articles

Improve Article
Save Article
Like Article

Graph Representation using Java ArrayList

  • Difficulty Level : Hard
  • Last Updated : 16 Apr, 2019

Prerequisite : Graph and its representations

In this article, we will be discussing Adjacency List representation of Graph using ArrayList in Java.

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.



Following is adjacency list representation of the above graph.

Adjacency List Representation of Graph

The idea is to use ArrayList of ArrayLists.




// Java code to demonstrate Graph representation
// using ArrayList in Java
import java.util.*;
  
class Test {
  
    static void addEdge(ArrayList<ArrayList<Integer> > adj,
                        int u, int v)
    {
        adj.get(u).add(v);
        adj.get(v).add(u);
    }
  
    static void printAdjacencyList(ArrayList<ArrayList<Integer> > adj)
    {
        for (int i = 0; i < adj.size(); i++) {
            System.out.println("Adjacency list of " + i);
            for (int j = 0; j < adj.get(i).size(); j++) {
                System.out.print(adj.get(i).get(j) + " ");
            }
            System.out.println();
        }
    }
  
    public static void main(String[] args)
    {
        // Creating a graph with 5 vertices
        int V = 5;
        ArrayList<ArrayList<Integer> > adj = new ArrayList<ArrayList<Integer> >(V);
        for (int i = 0; i < V; i++)
            adj.add(new ArrayList<Integer>());
  
        // Adding edges one by one.
        addEdge(adj, 0, 1);
        addEdge(adj, 0, 4);
        addEdge(adj, 1, 2);
        addEdge(adj, 1, 3);
        addEdge(adj, 1, 4);
        addEdge(adj, 2, 3);
        addEdge(adj, 3, 4);
        printAdjacencyList(adj);
    }
}
Output:
Adjacency list of 0
1 4 
Adjacency list of 1
0 2 3 4 
Adjacency list of 2
1 3 
Adjacency list of 3
1 2 4 
Adjacency list of 4
0 1 3

Similar Implementation using a separate Class for Graph.




// Java code to demonstrate Graph representation
// using ArrayList in Java
import java.util.*;
  
class Graph {
    ArrayList<ArrayList<Integer> > adj;
    int V;
    Graph(int v)
    {
        V = v;
        adj = new ArrayList<ArrayList<Integer> >(V);
        for (int i = 0; i < V; i++)
            adj.add(new ArrayList<Integer>());
    }
  
    void addEdge(int u, int v)
    {
        adj.get(u).add(v);
        adj.get(v).add(u);
    }
  
    void printAdjacencyList()
    {
        for (int i = 0; i < adj.size(); i++) {
            System.out.println("Adjacency list of " + i);
            for (int j = 0; j < adj.get(i).size(); j++) {
                System.out.print(adj.get(i).get(j) + " ");
            }
            System.out.println();
        }
    }
}
  
class Test {
  
    public static void main(String[] args)
    {
        // Creating a graph with 5 vertices
        int V = 5;
  
        Graph g = new Graph(V);
  
        // Adding edges one by one.
        g.addEdge(0, 1);
        g.addEdge(0, 4);
        g.addEdge(1, 2);
        g.addEdge(1, 3);
        g.addEdge(1, 4);
        g.addEdge(2, 3);
        g.addEdge(3, 4);
        g.printAdjacencyList();
    }
}
Output:
Adjacency list of 0
1 4 
Adjacency list of 1
0 2 3 4 
Adjacency list of 2
1 3 
Adjacency list of 3
1 2 4 
Adjacency list of 4
0 1 3



My Personal Notes arrow_drop_up
Recommended Articles
Page :

Start Your Coding Journey Now!