**What Is Graph List in Data Structure?**

In data structure, a graph is a non-linear data structure that consists of a set of vertices (also known as nodes) and a set of edges connecting these vertices. Graphs are widely used to represent various real-world scenarios such as social networks, transportation networks, and computer networks.

There are different ways to represent graphs, and one common representation is the graph list.

## Graph List

A graph list is a way to represent a graph using an adjacency list. An adjacency list is a collection of linked lists where each vertex has its own linked list containing its adjacent vertices.

This allows for efficient storage of the edges in the graph while also providing quick access to neighbors of a particular vertex.

Let’s say we have a graph with four vertices: A, B, C, and D. The adjacency list representation would look like this:

- A: B -> C
- B: A -> C -> D
- C: A -> B -> D
- D: B -> C

In this representation, each vertex has its own linked list containing its adjacent vertices. For example, vertex A has an adjacent vertex B and an adjacent vertex C. Vertex B has adjacent vertices A, C, and D. And so on.

## Advantages of Using Graph List

There are several advantages to using the graph list representation:

**Space Efficiency:**The graph list representation can be more space-efficient than other representations for sparse graphs (graphs with fewer edges). It only stores the necessary information about the edges.**Quick Neighbors Lookup:**With the graph list representation, it is easy to find the neighbors of a particular vertex.This allows for efficient traversal of the graph and can be useful in many graph algorithms.

**Ease of Modification:**The graph list representation makes it easy to add or remove edges from the graph. Adding or removing an edge only requires modifying the corresponding linked lists.

## Disadvantages of Using Graph List

While the graph list representation has its advantages, it also has some disadvantages:

**Space Inefficiency for Dense Graphs:**If the graph is dense (has many edges), the graph list representation may become space-inefficient. It requires storing a linked list for each vertex, which can result in a large amount of memory usage.**Inefficient Edge Existence Check:**Checking if an edge exists between two vertices in the graph list representation can be inefficient. It requires traversing through the linked lists to find if the vertices are connected.

### Conclusion

In summary, a graph list is a way to represent a graph using an adjacency list. It provides space efficiency for sparse graphs and allows for quick access to neighbors of a vertex.

However, it may become space-inefficient for dense graphs and checking edge existence can be inefficient. The choice of representation depends on the specific requirements of your application.