Difference Between Singly and Doubly Linked List
Have you ever wondered about the key differences between Singly and Doubly Linked Lists? The main difference lies in their structure, as Singly Linked Lists consist of nodes with a single pointer to the next node, making them efficient yet unidirectional. In contrast, Doubly Linked Lists include an extra pointer in each node pointing to the previous node, allowing bidirectional navigation but at the cost of increased memory usage. Let's understand more!
A Singly Linked List is a linear data structure where each element (called a node) contains some data and a pointer to the next node in the sequence. While, a Doubly Linked List is similar to a Singly Linked List but with an additional feature that each node contains a pointer to the next node as well as a pointer to the previous node. In this blog, we will understand the differences between them in detail!
Table of Content
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Difference Between Singly Linked List and Doubly Linked List
Below is a table of differences between singly and doubly linked lists.
| Feature |
Singly Linked List |
Doubly Linked List |
| Node Structure |
Each node contains data and a pointer to the next node. |
Each node contains data, a pointer to the next node, and a pointer to the previous node. |
| Traversal |
It can only be traversed in one direction: forward. |
It can be traversed in both directions: forward and backward. |
| Memory Usage |
Uses less memory per node (one pointer). |
Uses more memory per node (two pointers). |
| Implementation Complexity |
Simpler to implement compared to a doubly linked list. |
More complex to implement due to the additional backward link. |
| Operation Complexity |
Insertions and deletions are generally simpler at the beginning of the list or when a reference is already available to the node immediately preceding the target. |
Insertions and deletions are more efficient at both ends and in the middle, especially when the predecessor node is not known because you can navigate to it via the previous pointer. |
| Use Cases |
Suitable for simple applications where memory usage is critical and only forward traversal is needed. |
Preferred for complex applications where bidirectional traversal is necessary, such as navigating pages in a web browser history. |
| Examples |
Implementation of simple queues (FIFO structures). |
Implementation of navigation systems, undo functionality in applications, and more complex queues and stacks. |
What is a Singly Linked List?
A Singly Linked List is a fundamental data structure that consists of a sequence of elements, each contained in a "node." The key feature of a singly linked list is that every node contains a reference to the next node in the sequence, forming a linear and unidirectional chain of nodes from the first (head) to the last (tail).
Here's a Mind Map For Singly Linked List
What is a Doubly Linked List?
A Doubly Linked List is an advanced form of a linked list in which each node contains three components: the data, a pointer to the next node in the sequence, and a pointer to the previous node. This two-way linkage allows traversal of the list in both forward and backward directions, providing greater flexibility and efficiency in certain operations compared to a Singly Linked List.
Here's a Mind Map For Doubly Linked List
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Similarities Between Singly and Doubly Linked List
Here's a table highlighting the similarities between singly and doubly linked list
| Feature |
Similarity |
| Basic Structure |
Both consist of nodes that hold data and pointer(s) to connect sequentially with other nodes. |
| Dynamic Size |
Both can grow or shrink in size dynamically with the addition or removal of nodes, unlike static data structures like arrays. |
| Non-contiguous Storage |
Nodes are stored non-contiguously in memory and linked by pointers in both types of lists. |
| Linear Data Structure |
They represent a linear sequence of elements, with each node having a single successor (except the last node). |
| Element Access |
Direct access to elements is not possible, and elements are accessed sequentially, starting from the head (or tail, in doubly linked lists). |
| Insertion/Deletion Flexibility |
Both provide efficient insertion and deletion operations compared to array-based structures, especially when operating near the head or within the list (not requiring shifting of elements). |
| Use Cases |
Both are suitable for applications where dynamic memory allocation is preferred, and the cost of frequent insertions and deletions needs to be minimized. |
While both types of lists are used to store elements dynamically and provide flexibility in memory allocation and operations compared to static data structures like arrays, the choice between using a Singly or Doubly Linked List depends on the specific requirements of the application.
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FAQs
What is the main structural difference between singly and doubly linked lists?
The main structural difference lies in the node design. A node in a singly linked list contains data and a single pointer to the next node, facilitating forward traversal only. Conversely, a node in a doubly linked list contains data, a pointer to the next node, and an additional pointer to the previous node, allowing for both forward and backward traversal.
When would I choose a doubly linked list over a singly linked list?
Choose a doubly linked list when your application requires efficient backward traversal or operations that benefit from accessing the previous node directly, such as bidirectional navigation, or when you need to perform frequent insertions and deletions from both ends of the list. Doubly linked lists offer greater flexibility at the cost of increased memory usage due to the additional previous pointer in each node.
Is memory usage higher in doubly linked lists compared to singly linked lists?
Yes, memory usage is higher in doubly linked lists because each node contains an extra pointer to the previous node, effectively doubling the pointer memory requirement compared to singly linked lists. This makes singly linked lists more memory-efficient, albeit at the expense of some operational flexibility.
Can I perform backward traversal in a singly linked list?
No, singly linked lists do not inherently support backward traversal because each node only contains a pointer to the next node and lacks a reference to the previous node. Backward traversal or reverse access would require additional structures or algorithms, such as reversing the list or maintaining an external stack to simulate backward traversal, which would not be as efficient as the native backward traversal in doubly linked lists.
How do insertion and deletion operations compare in singly and doubly linked lists?
In singly linked lists, insertion and deletion operations are generally simple and efficient, especially at the beginning of the list or when a reference to the node immediately preceding the target is available. However, deleting a node without such a reference requires traversing the list from the beginning to find the preceding node. In contrast, doubly linked lists allow for more straightforward insertion and deletion at both ends and in the middle of the list, as nodes can easily be accessed and removed or added by leveraging the previous pointer, without the need for full traversal to find preceding nodes.
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