Introduction to Linked Lists and Types of Linked Lists | Data Structures and Algorithms Day #3

Introduction to Linked Lists and Types of Linked Lists | Data Structures and Algorithms Day #3

Learn what linked lists are, the types of linked lists (singly, doubly, and circular), and how to implement them using Python and JavaScript

In this article, we’ll explore linked lists in programming, their importance, and how they compare to other data structures like arrays. Linked lists are fundamental concepts in computer science, and understanding them helps programmers develop efficient algorithms and handle dynamic memory more effectively.

We’ll also look at different types of linked lists—singly, doubly, and circular linked lists—and see how they differ. Finally, we’ll provide code examples in Python and JavaScript to demonstrate how to perform common linked list operations like insertion and traversal.


What is a Linked List?

A linked list is a linear data structure in which elements, called nodes, are connected using pointers. Each node consists of two parts:

  1. Data: The value stored in the node.

  2. Pointer (or reference): A link to the next node in the list.

Unlike arrays, linked lists don’t require contiguous memory allocation, making them more efficient for operations where the data size is dynamic.


Why Use Linked Lists?

Here are some of the advantages linked lists offer over arrays:

  • Dynamic Size: Linked lists can grow or shrink as needed without requiring memory reallocation.

  • Efficient Insertions/Deletions: Adding or removing elements in the middle of a linked list is faster since there’s no need to shift elements.

  • Memory Management: Since linked lists use pointers, they are better suited for fragmented memory allocation systems.

Use Cases of Linked Lists:

  • Implementing stacks and queues

  • Handling undo functionality in text editors

  • Managing browser history (back/forward actions)


Types of Linked Lists

There are three common types of linked lists: singly linked lists, doubly linked lists, and circular linked lists. Below, we’ll explore each type and its characteristics.

1. Singly Linked List

Each node points to the next node in a singly linked list, forming a one-way chain. The last node in the list points to null, indicating the end of the list.

Example in Python:

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

class SinglyLinkedList:
    def __init__(self):
        self.head = None

    def insert_at_beginning(self, data):
        new_node = Node(data)
        new_node.next = self.head
        self.head = new_node

    def traverse(self):
        current = self.head
        while current:
            print(current.data, end=" -> ")
            current = current.next
        print("None")

# Usage
ll = SinglyLinkedList()
ll.insert_at_beginning(3)
ll.insert_at_beginning(5)
ll.traverse()

Example in JavaScript:

class Node {
    constructor(data) {
        this.data = data;
        this.next = null;
    }
}

class SinglyLinkedList {
    constructor() {
        this.head = null;
    }

    insertAtBeginning(data) {
        const newNode = new Node(data);
        newNode.next = this.head;
        this.head = newNode;
    }

    traverse() {
        let current = this.head;
        while (current) {
            process.stdout.write(`${current.data} -> `);
            current = current.next;
        }
        console.log('null');
    }
}

// Usage
const ll = new SinglyLinkedList();
ll.insertAtBeginning(3);
ll.insertAtBeginning(5);
ll.traverse();

2. Doubly Linked List

A doubly linked list has nodes that contain two pointers—one pointing to the next node and another to the previous node. This makes both forward and backward traversal possible.

Key Advantages:

  • Efficient deletions from both ends.

  • Easier reversal of the list.


3. Circular Linked List

In a circular linked list, the last node points to the first node, forming a loop. Circular linked lists can be either singly or doubly linked, depending on whether each node points to one or two other nodes.

Applications:

  • Round-robin scheduling in operating systems.

  • Buffer management in streaming data.


Comparison: Singly vs. Doubly vs. Circular Linked Lists

FeatureSingly Linked ListDoubly Linked ListCircular Linked List
Memory usageLowHighVaries
Direction of traversalForward onlyForward and backwardForward or both
Insertion at endInefficientEfficientEfficient
Loop possibilityNoNoYes

Common Misconceptions about Linked Lists

  1. "Linked lists are always better than arrays."

    • Not necessarily. Arrays are more efficient for random access since elements are indexed.
  2. "All linked lists are difficult to implement."

    • With practice, linked list operations become intuitive.
  3. "Linked lists use too much memory."

    • Although pointers increase memory usage, this tradeoff is beneficial when handling dynamic data.

FAQs about Linked Lists

Q1: What are the advantages of linked lists over arrays?

  • Linked lists offer dynamic size and faster insertions and deletions.

Q2: When should I use a doubly linked list?

  • Use a doubly linked list when you need bidirectional traversal or frequent deletions from both ends.

Q3: Are circular linked lists practical?

  • Yes, especially in round-robin scheduling and real-time systems.

Conclusion

Linked lists are a powerful data structure that offer flexibility and efficiency in memory management and data manipulation. By understanding the types of linked lists—singly, doubly, and circular—you’ll know which one to choose for different programming scenarios.

Now that you’ve grasped the basics, try implementing your own linked list in your favorite programming language. In our upcoming articles, we’ll dive deeper into linked list algorithms and explore common use cases in software development.


Explore other essential data structures, such as arrays and stacks, in our Introduction to Arrays and Operations article.