Adjacency List meaning & definition in DSA

Last Updated : 01 Aug, 2023

An adjacency list is a data structure used to represent a graph where each node in the graph stores a list of its neighboring vertices.

Graph representation of Directed Graph to Adjacency List

Characteristics of the Adjacency List:

The size of the matrix is determined by the number of nodes in the network.
The number of graph edges is easily computed.
The adjacency list is a jagged array.

How to build an Adjacency List?

It is very easy and simple to construct an adjacency list for a graph there are certain steps given below that you need to follow:

Create an array of linked lists of size N, where N is the number of vertices in the graph.
Create a linked list of adjacent vertices for each vertex in the graph.
For each edge (u, v) in the graph, add v to the linked list of u, and add u to the linked list of v if the graph is undirected otherwise add v to the list of u if it is directed from u to v. (In case of weighted graphs store the weight along with the connections).

Applications of the Adjacency List:

Graph algorithms: Many graph algorithms like Dijkstra’s algorithm, Breadth First Search, and Depth First Search use adjacency lists to represent graphs.
Image Processing: Adjacency lists can be used to represent the adjacency relationships between pixels in an image.
Game Development: These lists can be used to store information about the connections between different areas or levels the game developers use graphs to represent game maps or levels.

Advantages of using an Adjacency list:

An adjacency list is simple and easy to understand.
Adding or removing edges from a graph is quick and easy.

Disadvantages of using an Adjacency list:

In adjacency lists accessing the edges can take longer than the adjacency matrix.
It requires more memory than the adjacency matrix for dense graphs.

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Adjacency matrix meaning and definition in DSA

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