Linked List

Back to: Python Data Structure and Algorithims

Welcome to Linked Lists

Let’s begin our journey into data structures with one of the most fundamental concepts — the Linked List.
Before we understand what a linked list is, let’s first recall something familiar — a Python list.

🧠 Understanding a Normal Python List

In Python, when we create a list like this:

This list has indexes and is stored in a contiguous block of memory.
That means all its elements are placed right next to each other in memory, something like this:

💡 Because the elements are stored together, we can quickly access any element using its index:

This is called O(1) time access, meaning it takes constant time to retrieve any element.

🔗 Moving from Lists to Linked Lists

Now, let’s transform our Python list into a Linked List step by step.

🟣 Step 1: Remove Indexes

A linked list doesn’t use indexes.
Instead, each element (called a node) knows only about the next node in the sequence.

So, instead of:

We’ll have something like:

Each arrow (→) represents a link or a pointer from one node to the next.

⚙️ Step 2: Nodes and Pointers

In a linked list:

• Each element is called a Node.

• Each Node has:

  • Data (the actual value, like 10, 20, etc.)

  • Next pointer (the address of the next node)

Here’s a small Python class to represent a Node:

Now, we can link nodes manually:

So in memory, it looks like this:

🧩 Step 3: Head and Tail

To work with a linked list, we use two special pointers:

• Head → Points to the first node

• Tail → Points to the last node

Example:

Diagrammatically:

The last node’s next is None, indicating the end of the list.

🧬 Step 4: Linked List in Memory

Unlike Python lists, linked lists are not stored in contiguous memory.
The nodes can be scattered anywhere in memory — but since each node knows where the next one is, we can still traverse the list.

Imagine memory blocks like this:

So even though the data isn’t side-by-side, we can follow the links to reach every node.

⚡ Python List vs Linked List — Key Differences

🧰 Example: Traversing a Linked List

Let’s print all values in our linked list:

Output:

🧩 Summary

• A Linked List is a chain of nodes connected through pointers.

• It has a head (start) and a tail (end).

• It does not store elements in contiguous memory.

• Accessing elements is slower than lists, but inserting or deleting elements is easier.