Introduction

Doubly Linked List is an important topic in Data Structures and Algorithms (DSA) and is frequently asked in coding interviews. If you are enrolled in a DSA course in Jaipur, understanding doubly linked lists will help you handle complex data traversal problems efficiently.

Unlike singly linked lists, doubly linked lists allow traversal in both directions.

What is a Doubly Linked List?

A Doubly Linked List is a linear data structure where each node contains:

• Data
• Pointer to previous node (prev)
• Pointer to next node (next)

Structure of Node

Each node contains:

• prev → points to previous node
• data → stores value
• next → points to next node

Example:
NULL ← 10 ⇄ 20 ⇄ 30 ⇄ 40 → NULL

Key Features

• Bidirectional traversal
• Easy insertion and deletion
• More flexible than singly linked list

Operations in Doubly Linked List

1. Insertion

• At beginning
• At end
• At specific position

2. Deletion

• From beginning
• From end
• From specific position

3. Traversal

• Forward traversal
• Backward traversal

Time Complexity

O(1), O(n)

• Insertion → O(1) (at head/tail)
• Deletion → O(1)
• Traversal → O(n)

Advantages of Doubly Linked List

• Traversal in both directions
• Efficient deletion (no need to track previous node)
• Flexible operations

Disadvantages

• Extra memory for prev pointer
• More complex implementation
• Slightly slower than singly linked list

Doubly Linked List vs Singly Linked List

• Doubly has prev and next pointers
• Singly has only next pointer
• Doubly supports backward traversal
• Singly uses less memory

Real-World Applications

• Navigation systems (forward/backward)
• Browser history
• Undo/Redo operations
• Music playlist navigation

Common Interview Questions

• Insert in doubly linked list
• Delete a node
• Reverse doubly linked list
• Convert singly to doubly linked list

Best Practices

• Handle NULL pointers carefully
• Update both prev and next pointers
• Test edge cases
• Practice pointer manipulation

Summary

• Doubly linked list has two pointers
• Supports bidirectional traversal
• More flexible than singly linked list
• Slightly higher memory usage
• Important for coding interviews

FAQs

Q1. What is doubly linked list?
A linked list where each node has prev and next pointers.

Q2. What is advantage over singly linked list?
It allows backward traversal.

Q3. What is time complexity of insertion?
O(1) at head or tail.

Q4. Why is it more memory intensive?
Because it stores an extra pointer.

Q5. Is it important for interviews?
Yes, it is a common data structure.

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