When is Doubly Linked List more Efficient than Singly Linked List?

Did you know there are some cases where a Doubly Linked List is more efficient than a Singly Linked List, even though it takes more memory compared to a Singly Linked List? What are those Cases? Well, we will discuss that in the following article, But first, let’s talk about Singly and linked lists:

What is a Singly Linked List?

A singly linked list is a linear data structure in which the elements are not stored in contiguous memory locations and each element is connected only to its next element using a pointer.

In a singly linked list, each node contains a reference to the next node in the sequence. Traversing a singly linked list is done in a forward direction. To know more, please refer to the Singly Linked list.

What is a Doubly Linked List?

A doubly linked list (DLL) is a special type of linked list in which each node contains a pointer to the previous node as well as the next node of the linked list.

In a doubly linked list, each node contains references to both the next and previous nodes. This allows for traversal in both forward and backward directions, but it requires additional memory for the backward reference. To know more, please refer to Doubly Linked List.

When is a Doubly linked list more efficient than a singly linked list?

Doubly linked lists are more efficient than singly linked lists in the following cases:

In Bi-directional Traversals:

• Doubly linked lists allow for traversal in both the forward and backward directions, while singly linked lists only allow for forward traversal.
• This can be useful for applications where it is necessary to traverse the list in both directions, such as a web browser’s history list or a music player’s playlist.

Deletion of a given node:

• Since Doubly Linked Lists have two pointers for each node, it is possible to delete a node of the list without having to traverse the entire list.
• This can be significantly faster than deleting an element in a singly linked list, which requires traversing the list from the beginning until the element is found because we need previous pointer to reconnect the singly linked list.
• Doubly linked lists are more efficient than singly linked lists in this case because they have two pointers for each node, one to the next node and one to the previous node, and we don’t need to traverse the linked list now .
• This allows for direct access of node and its adjacent nodes, which means that this operation can be performed in O(1) time, regardless of the length of the list.

When implementing other data structures, such as stacks and queues:

• Doubly linked lists can be used to implement stacks and queues very efficiently. In fact, doubly linked lists are the preferred data structure for implementing these data structures in many programming languages.
• Few examples, where doubly linked list might be preferred are:
  • Deque Operations: Doubly linked lists are used in implementing deque (double-ended queue) data structures efficiently. Deque supports insertion and deletion from both ends in constant time with a doubly linked list. This makes operations like enqueue and dequeue in a queue or push and pop in a stack more efficient when implemented using a doubly linked list.
  • Memory Allocation and Deallocation: Doubly linked lists can be helpful in memory management scenarios where you need to allocate and deallocate memory blocks dynamically. When deallocating memory blocks, if you have a reference to a node in a doubly linked list, you can remove it in constant time, making memory deallocation more efficient compared to singly linked lists.
  • Undo Operations: Doubly linked lists are useful for implementing undo functionality in applications. Each operation can be stored as a node, and moving backward (undo) or forward (redo) in the history is efficient with the bidirectional pointers in a doubly linked list.

Conclusion:

Doubly linked lists are more efficient than singly linked lists in terms of performance, but they also require more memory. Doubly linked lists are often used in applications where performance is a critical concern, such as web browsers, operating systems, and databases. However, they are not as widely used as singly linked lists, which are simpler to implement and require less memory. The best choice for a particular application will depend on the specific requirements of that application.