Graph traversal and Graph traversal algorithm

What is graph traversal?

It refers to the process of visiting (checking and/or updating) each vertex (node) in a graph.
A smaller graph seems relatively easy to traverse. But when it comes to traversing a graph with a huge number of nodes, the process needs to be automated.
Sequences of steps that are used to traverse a graph are known as graph traversal algorithms. There are two algorithms that are used for traversing a graph
1. Breadth-First Search
2. Dept First Search

Terminologies we need to familiarise ourselves with

Exploring a vertex (node) :
- Means visiting all the connected vertices.
- Follow the illustration of the graph mentioned below.

We'll use this for understanding the breadth-first search.

In breadth-first search, we use the queue data structure
Here, suppose we start with node 0 and put it in the list of visited nodes, then we visit nodes 2 and 1 since they are directly connected to node 0.
And then gets visited node 3 and 4.
So, the order of exploring would be 0, 2, 1, 3, 4.
In breadth-first serach, we visit from left to right all the nodes which lie on the same level.
Here, node 0 was on one level, followed by nodes 2 and 1, and then nodes 3 and 4.

Using below mentioned illustration we'll understand depth-first search
In depth-first search, we use the stack data structure.
Here, suppose we start with 0 and put it in the list of visited nodes, then we visit node 2 and then visit nodes further connected to node 2.
So, we visit node 3 and since it is further connected to node 1 and node 1 is connected to 4, we'll follow them in the same order.
So, the order of exploring would be 0, 2, 3, 1, 4.
In depth first search, we visit from top to down all the nodes which are connected with each other.
Here, node 0 was the parent, which is connected to node 2, which is again connected to node 3, and then node 1 and then node 4.