Traversing a Single Linked List (Counting the Nodes)

Summary

This presentation teaches how to traverse a single linked list and count its nodes. It explains that traversal involves visiting each node until the end is reached. The script provides a step-by-step explanation of a program that uses a 'count_of_nodes' function to calculate the total number of nodes by iterating through the list using a pointer. It emphasizes the importance of creating the linked list before calling the function and concludes by hinting at an alternative method to be discussed in a future lecture.

Takeaways

• 🔍 **Traversing a Single Linked List**: Visiting each node of the list until the end node is reached.
• 📈 **Application of Traversal**: Counting the number of nodes in the list is a practical application of traversal.
• 💡 **Understanding the Concept**: Traversing means reaching every node using the head pointer until the end.
• 📝 **Program Structure**: The program includes necessary header files and a struct node, along with a main function.
• 🔧 **Function Usage**: The `count_of_nodes` function is used to count nodes by traversing the list.
• 🔑 **Head Pointer**: The head pointer is crucial as it points to the first node and is passed to the counting function.
• 🌐 **LinkedList Creation**: Before traversing, a single linked list must be created.
• 🔄 **Traversal Process**: The traversal loop continues until the pointer (`ptr`) becomes NULL, incrementing the count for each node visited.
• 📊 **Counting Mechanism**: A counter variable is used to keep track of the number of nodes visited.
• 📖 **Code Simplification**: There's mention of an alternative way to write the traversal code, to be discussed in a subsequent lecture.

Q & A

What does traversing a single linked list mean?

Traversing a single linked list means visiting each node of the list until the end node is reached.

What is the purpose of traversing a linked list in the context of the presentation?

The purpose of traversing a linked list in the presentation is to count the total number of nodes in the list.

What are the header files required for the program mentioned in the script?

The header files required for the program are stdio.h and stdlib.h.

What is the significance of the 'head' pointer in the context of the script?

The 'head' pointer is significant because it points to the first node of the linked list.

What does the 'count_of_nodes' function do?

The 'count_of_nodes' function counts the number of nodes in the linked list by traversing it.

How is the 'count' variable used in the 'count_of_nodes' function?

The 'count' variable is used to keep track of the number of nodes visited during the traversal of the linked list.

What does the condition 'if head is equal to NULL' imply in the script?

The condition 'if head is equal to NULL' implies that the linked list is empty and has no nodes.

What is the role of the 'ptr' pointer in the traversal process?

The 'ptr' pointer is used to traverse the list by pointing to each node and moving to the next node until it reaches the end of the list.

How does the while loop contribute to the traversal of the linked list?

The while loop runs until 'ptr' becomes NULL, which means it continues to traverse the list until the end node is reached.

What is the output of the program when the linked list contains three nodes?

The output of the program when the linked list contains three nodes is 'three', indicating that three nodes have been counted.

Is there an alternative way to write the code for counting nodes in a linked list as suggested in the script?

Yes, the script suggests that there is another way to write the code for counting nodes in a linked list, which will be discussed in the next lecture.

Outlines

00:00

🔍 Introduction to Single Linked List Traversal

This paragraph introduces the concept of traversing a single linked list, which involves visiting each node in the list until the end node is reached. The purpose of traversal is explained with an example of counting the number of nodes in the list. The presenter assumes the existence of a linked list and aims to calculate the total number of nodes using a 'count_of_nodes' function. The explanation includes the importance of including header files 'stdio.h' and 'stdlib.h' and defining a 'struct node'. The main function is described as the starting point of the program, where the 'count_of_nodes' function is called, passing the 'head' pointer. The 'head' pointer's role is explained as pointing to the first node of the list, and the necessity of creating the linked list before calling the function is emphasized. The paragraph concludes with a brief overview of the function's code, which initializes a 'count' variable to zero and includes a check for an empty list.

05:01

🔄 Traversal Process and Counting Nodes

This paragraph delves into the mechanics of the 'count_of_nodes' function, detailing how it traverses the linked list and counts the nodes. It starts by initializing a pointer 'ptr' to NULL and then assigning it the value of 'head', which points to the first node. A while loop is introduced that continues until 'ptr' becomes NULL, signifying the end of the list. Inside the loop, the 'count' variable is incremented each time a node is visited, and 'ptr' is updated to point to the next node using 'ptr->link'. The process is illustrated with hypothetical addresses to clarify how 'ptr' moves through the list. The paragraph concludes with a discussion of an alternative way to write the code, which will be explored in a subsequent lecture. The presenter summarizes the outcome of the traversal by printing the 'count', which represents the total number of nodes visited, and thanks the audience for their attention.

Keywords

💡Traversing

Traversing refers to the process of visiting each element in a data structure, such as a linked list, to perform operations or gather information. In the context of the video, traversing a single linked list means visiting each node from the beginning until the end node is reached. This is crucial for understanding the structure and contents of the list, and it is used to count the number of nodes in the list. For example, the script mentions that 'Traversing a single linked list means visiting each node of a single linked list until the end node is reached'.

💡Single Linked List

A single linked list is a linear data structure where each element is a separate object, called a node, and each node contains a reference to the next node in the sequence. The video script uses the single linked list as an example to demonstrate the concept of traversing, where the head pointer points to the first node of the list, and traversal is done until the end of the list is reached.

💡Node

A node is a fundamental building block of a linked list, consisting of data and a reference (or pointer) to the next node in the sequence. The video script explains that the process of traversing a linked list involves visiting each node until the end node is reached, emphasizing the importance of nodes in the structure of a linked list.

💡Head Pointer

The head pointer is a reference to the first node in a linked list. It is used to begin the traversal process. The script mentions that 'The head pointer is pointing to the first node of the list', which is essential for starting the traversal and accessing the list.

💡Counting Nodes

Counting nodes is the process of determining the number of elements in a linked list by traversing it. The video script describes this process as an application of traversing a single linked list, where a counter variable is incremented for each node visited until the end of the list is reached, thus counting the total number of nodes.

💡Empty List

An empty list is a linked list with no nodes. In the script, it is mentioned that if the head pointer is equal to NULL, it indicates that the linked list is empty, as the head is not pointing to any node, which is a crucial check before attempting to traverse the list.

💡Pointer

A pointer is a variable that stores the memory address of another variable. In the context of the video, pointers are used to navigate through the nodes of a linked list. The script explains that a pointer is initialized to NULL and then assigned the value of the head to point to the first node of the list.

💡Struct Node

Struct Node refers to a structure in programming that defines the format of a node in a linked list, typically containing data and a pointer to the next node. The video script mentions that 'We should have this struct node as well', indicating that it is a fundamental part of creating and working with linked lists.

💡Main Function

The main function is the entry point of a program in many programming languages. In the script, the main function is where the program starts and calls the count_of_nodes function to perform the traversal and counting of nodes in the linked list.

💡While Loop

A while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. In the video script, a while loop is used to continue traversing the list as long as the pointer is not NULL, effectively counting the nodes until the end of the list is reached.

💡NULL

NULL is a null pointer in programming that indicates the absence of a valid memory address. In the context of the video, NULL is used to check if the head pointer or the pointer currently being used for traversal is at the end of the list, as the end of a linked list is typically represented by a NULL pointer.

Highlights

Introduction to traversing a single linked list

Traversing a linked list involves visiting each node until the end node is reached

Application of traversing a single linked list: counting the number of nodes

Assumption of having a pre-existing linked list for traversal

The head pointer is used to point to the first node of the list

The purpose of the program is to calculate the total number of nodes in the list

The necessity of including stdio.h and stdlib.h header files

The struct node is required for the program

The main function is the starting point of the program

The count_of_nodes function is called to count the nodes

The head pointer is passed to the count_of_nodes function

Explanation of the head pointer's role in traversing the list

The importance of creating a single linked list before calling count_of_nodes

The count_of_nodes function's code explanation

Initialization of the count variable to zero for counting nodes

Checking if the head is NULL to determine if the list is empty

Using a while loop to traverse the list until ptr becomes NULL

Incrementing the count variable for each visited node

Accessing the link part of the node to move to the next node

Termination of the loop when ptr becomes NULL

Printing the final count of nodes after exiting the loop

Alternative ways of writing the code for traversing and counting nodes

Conclusion and thanks for watching the presentation

Transcripts

In this presentation, we will learn

how to traverse a single linked list

and we will also see one application of

traversing a single linked list that is, counting the number of nodes.

So, let's get started.

First, we will try to understand what is the meaning

of traversing a single linked list.

Traversing a single linked list means visiting each node

of a single linked list until the end node is reached.

Which means that you are visiting each node of a list

until the end node is reached.

For the sake of simplicity, we will consider this example.

That is, we will assume that we already have this list

and we need to traverse this list.

Not only we need to traverse this list,

we also have to calculate the total number of nodes

in this list by traversing this linked list. Okay.

So, we will assume that we have this linked list already.

The head pointer is pointing to the first node of the list.

And our job is to calculate the total number of nodes in this list.

For this purpose, I am writing this program.

Here in this program, we should have

these two header files as stdio.h and stdlib.h.

We should have this struct node as well.

And apart from this, this main function,

which is the starting point of the program.

And here, we are basically calling this count_of_nodes function

which will count the number of nodes in the list.

And here, I'm passing this head pointer

which I haven't declared over here.

So, what is this head basically?

This head is the pointer which is

pointing to the first node of the list.

We need to imagine that head is the pointer

which is the pointer to the first node of the linked list shown here.

I am not writing the complete code over here.

Okay, you already know how to create a single linked list.

The first job is obviously to create

a single link list like this.

And then after that, we will call this count_of_nodes function.

And here, we need to pass this head pointer.

This pointer is enough.

Because, this is pointing to the first node of the list.

And we already know, with the help of head pointer,

we can actually reach every node of the list.

So, we need to pass the head pointer

of this list to this count_of_nodes function.

But you should always remember that

we first have to create this single linked list.

Then after that, we can call this count_of_notes function.

I'm calling this directly because I'm assuming

that this single linked list I've already created,

and there is no need to create this again.

So, this is not a complete code, by the way.

Okay, because our focus is to understand

count_of_nodes function and nothing else.

Now, here is the function which consists of these line of code.

Now, let's try to understand this

particular piece of code properly.

Here, we are declaring this count variable,

which consists of this value zero.

This is the initial point, count contains zero.

Okay. Basically, this variable is used to count

the number of nodes in the list.

That is why, I call this variable count.

After this, we have this piece of code,

which says that if head is equal to NULL,

then we will print linked list is empty.

head is the pointer which is pointing

to the first node of the list, right?

If head contains NULL, that means

it is not pointing to anything.

And this simply means that linked list is empty.

That is why, we have to print linked list is empty.

If this is not satisfied,

as you can see over here, this is not satisfied.

head must contain the address of the first node of the list.

Because, our list is not empty.

So, definitely we will reach this point of code.

That is, we will create a pointer of type struct node

and we will initialize it to NULL.

After that, we will put the value of head inside this ptr.

That means, we know that head contains 1000.

So, this NULL will also get replaced by 1000.

This is what this line says.

Because of this, ptr will point to the first node of the list.

After that, we have this piece of code

which will run until ptr becomes NULL.

This is the while loop, which will run until ptr becomes NULL.

Right now, ptr contains the address 1000

which is the address of the first node of the list.

When ptr contains NULL,

then we get outside of this loop, and we will print the count.

Let's see how this code works

and how it is helping us to traverse the list.

First, of course, we need to check this particular piece of code.

Here, ptr should not be equal to NULL.

We know that ptr contains the address 1000

and it is not equal to NULL.

Therefore, we can get inside this while loop and

will increment the value of count.

This means that the zero will get replaced by one.

And this simply means that the first node has been visited.

This count variable is keeping the

count of the number of nodes, right?

This one indicates that first node has been reached.

After that, with the help of ptr,

I am accessing the link part of this node,

which means that this can be replaced by 2000.

And eventually, ptr will contain this address 2000.

This means that now, ptr has been assigned with this address 2000,

which eventually says that this ptr

will now point to the second node of the list.

Because, it contains the address 2000.

After that, we will again check, is ptr equal to NULL.

No, ptr is still not equal to NULL, right.

We get inside this while loop,

will increment the count,

which means that now the second node has been reached

and you can clearly see that ptr has reached the second node.

So, it is clear from this fact that second node has been reached.

After that, we will again implement this statement.

ptr equal to ptr pointer link.

We know that ptr->link gives the link part of this node,

which means now, this can be replaced by 3000.

And eventually ptr contains the address 3000

after this line of code.

Now, it will point to the third node of the list.

After that we will again check this condition -

Is ptr equal to NULL?

Still, it is not equal to NULL, we get inside

increment the count. Now, count can be replaced by three

and then after that, we will access the ptr->link.

That is, we will access the link part of this node,

which contains NULL. So, this can be replaced by NULL.

And now ptr contains NULL.

Again we will check this condition, is ptr equal to NULL?

Yes, ptr is equal to NULL.

So, we will get outside of this loop, right?

Because, here this condition becomes false.

ptr not equal to NULL is actually false.

Because ptr contains NULL.

Therefore, we will get outside of this loop,

and we will print the count that is three.

So output is three.

Although, let me tell you that

there is another way of writing this code.

Instead of writing this whole code,

I can replace this with another code,

which we will see in the next lecture.

Okay friends, this is it for now.

Thank you for watching this presentation.