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# Difference between Singly and Doubly Linked List

Last Updated on July 27, 2023 by Mayank Dham

Linked lists are fundamental data structures used in computer programming to efficiently store and organize collections of elements. Among the various types of linked lists, two primary variations are the singly linked list and the doubly linked list. Both structures serve distinct purposes and offer unique advantages, making them essential tools for data manipulation in various programming scenarios. Before discussing the difference between singly and doubly linked lists, Letâ€™s understand what a singly linked list is.

A Singly Linked List is a linear data structure that consists of a sequence of nodes. Each node in a Singly Linked List contains two components: a data element and a pointer that points to the next node in the sequence. The first node in the sequence is called the head, and the last node is called the tail. If a node’s pointer is null, it means that it is the last node in the sequence.

To traverse a Singly Linked List, you start from the head and follow the pointers until you reach the end of the list. Inserting a new node into a Singly Linked List involves updating the pointer of the previous node to point to the new node, and updating the pointer of the new node to point to the next node. Deleting a node involves updating the pointer of the previous node to point to the next node, and freeing the memory of the deleted node.

A Doubly Linked List is a type of data structure that consists of a sequence of nodes, each containing two pointers instead of one as in Singly Linked List. Each node in a Doubly Linked List has three components: a data element, a pointer to the next node, and a pointer to the previous node. The pointer to the previous node is what makes a Doubly Linked List different from a Singly Linked List.

Inserting a new node into a Doubly Linked List involves updating the pointers of the previous and next nodes to point to the new node, and updating the pointers of the new node to point to the previous and next nodes. Deleting a node involves updating the pointers of the previous and next nodes to bypass the deleted node, and freeing the memory of the deleted node.

In this blog section, we will discuss the difference between singly linked list and doubly linked list.

A Singly Linked has nodes with a data field and a next link field. A Doubly Linked List has a previous link field along with a data field and a next link field.
In a Singly Linked List, the traversal can only be done using the link of the next node. In a Doubly Linked List, the traversal can be done using the next node link as well as the previous node link.
A Singly Linked List occupies less memory than the Doubly Linked List, as it has only 2 fields. A Doubly Linked List occupies more memory than the Singly Linked List, as it has 3 fields.
Accessing elements in a Singly Linked List is less efficient when compared to a Doubly Linked List, as only forward traversal is possible. Accessing elements in a Doubly Linked List is more efficient when compared to a Singly Linked List as both forward and backward traversal is possible.
The time complexity of inserting or deleting a node at a given position (if the pointer to that position is given) in a singly linked list is O(n). The time complexity of inserting or deleting a node at a given position (if the pointer to that position is given) in a doubly linked list is O(1).
Singly linked list is preferred when we have memory limitation(we canâ€™t use much memory) and searching is not required. Doubly linked list is preferred when we donâ€™t have memory limitation and searching is required(we need to perform search operation on the linked list).

Conclusion
In conclusion, we have discussed in this article, the difference between Singly Linked List and Doubly Linked List. While Singly Linked List has only one pointer per node and allows for forward traversal only, Doubly Linked Lists have two pointers per node and allow for both forward and backward traversal. It is important to understand the difference between singly linked list and a doubly linked list to choose the appropriate one for a given problem.

## FAQs

Q1: How do you insert a node at the beginning of a Doubly Linked List?
Ans: To insert a node at the beginning of a Doubly Linked List, you create a new node, set its next pointer to the current head of the list, set its previous pointer to NULL, and then set the head of the list to point to the new node.

Q2: Can you traverse a Singly Linked List in reverse order?
Ans: No, you cannot traverse a Singly Linked List in reverse order because each node has only one pointer that points to the next node.

Q3: Is there any difference between singly linked list and doubly linked list based on memory?
Ans: Yes, there is a difference between singly and doubly linked lists based on memory. Doubly-linked lists require more memory than singly-linked lists because each node in a doubly-linked list has an extra pointer to its previous node, whereas nodes in a singly-linked list only have a pointer to their next node.

Q4: Which data structure is better for implementing a stack between Singly Linked List and Doubly Linked List?
Ans: A Singly Linked List is better for implementing a stack since it requires less memory and provides the necessary functionality for a stack, which only requires insertion and deletion at one end.

Q5: Is there any difference between singly and doubly linked lists on the basis of the direction of traversal?
Ans: Yes, there is a difference between singly and doubly linked lists on the basis of the direction of traversal. Singly-linked lists can only be traversed in one direction, typically from the first node to the last node, while doubly-linked lists can be traversed in both directions, either from the first node to the last node or from the last node to the first node.