Difference between Singly linked list and Doubly linked list

Singly linked lists and doubly linked lists are two fundamental types of linked list data structures. A singly linked list each node contains data and a pointer to the next node in the sequence. In contrast, a doubly linked list each node includes data, a pointer to the next node, and an additional pointer to the previous node. Below, we explore the major distinctions between these two types of linked lists.

 Singly Linked List

A singly linked list is a sequence of nodes, where each node consists of two components: one for storing data and the other for holding a reference to the next node in the list.

Singly Linked List

  • The data section contains the actual value or information,
  • while the next is the reference or link section which stores the memory address of the next node.

Doubly Linked List

A doubly linked list is a variation of a linked list where each node includes two references, justifying its name. Each node in a doubly linked list has three parts: one for data and two pointers. One pointer refers to the previous node in the sequence, and the other points to the next node, enabling bidirectional navigation through the list.

Doubly Linked List

  • Data: Stores the actual information (e.g., 10, 20, A, Z etc).
  • Previous Pointer: Points to the previous node (e.g., NULL for the first node).
  • Next Pointer: Points to the next node in the sequence (e.g., address of the next node).

Common operations such as insertion, deletion, and traversal can be efficiently performed on a doubly linked list.

Node Structure of Singly Linked List Vs Doubly Linked List

  • Node Structure of Singly Linked List: Each node contains data and a pointer to the next node, enabling one-way traversal.
  • Node Structure of Doubly Linked List: Each node contains data, a pointer to the previous node, and a pointer to the next node, allowing two-way traversal.

Node Structure of Singly Linked List Vs Doubly Linked List

Difference between Singly Linked List and Doubly Linked List

Here are key differences between singly linked lists and doubly linked lists:

S. No. Singly Linked List Doubly Linked List
1 A singly linked list consists of two parts: one for storing data and the other as a pointer to the next node. A doubly linked list consists of three parts: one for data storage and two pointers (one pointing to the previous node and the other to the next node).
2 Traversal in a singly linked list is possible in only one direction. Traversal in a doubly linked list is possible in both forward and backward directions.
3 Singly linked lists are typically used in the implementation of stacks. Doubly linked lists are suitable for implementing structures like binary trees, heaps, and sometimes stacks.
4 When memory optimization is critical and searching is not required, singly linked lists are preferred. Doubly linked lists are better suited for scenarios requiring efficient searching and more complex operations.
5 Singly linked lists require less memory compared to doubly linked lists. Doubly linked lists consume more memory due to the extra pointer for bidirectional traversal.
6 Deleting the end (last) node requires traversal of the entire list. Deleting the last node is faster because the previous node’s pointer is already available by using a tail pointer (if maintained).
7 Reversing a singly linked list is complex and requires additional traversal and pointer adjustments. Reversing a doubly linked list is simpler due to its bidirectional links.
8 It is not possible to directly navigate to the previous node without traversing from the head. Direct access to the previous node is possible using the backward pointer  ( tail pointer if maintained).
9 Ideal for applications requiring sequential data processing, like implementing queues. Better for applications that involve frequent insertions, deletions, or bidirectional traversals, like a text editor’s undo/redo feature.
10 Singly linked lists are less suitable for circular implementations due to unidirectional traversal. Doubly linked lists are often preferred for circular data structures as both directions are accessible.
11 Searching for elements always starts from the head node and requires sequential traversal. Searching can be optimized in certain cases by starting from either the head or tail node.
12 Singly linked lists are simpler to implement and manage. Doubly linked lists are more complex due to the need to maintain two pointers per node.
13 In a singly linked list, insertion and deletion operations have a time complexity of O(n). In a doubly linked list, insertion and deletion operations have a time complexity of .