Why is a doubly linked list more useful than a singly linked list?

Singly Linked List vs Doubly Linked List

Before looking at the differences between the singly linked list and doubly linked list, we first understand what is singly linked list and doubly linked list separately.

Advantages, Disadvantages, and uses of Doubly Linked List

A Doubly Linked List(DLL) is a linear data structure that contains an extra pointer, typically called the previous pointer, together with the next pointer and data which are there in a singly linked list. Below is the image to illustrate the same.

Advantages Of DLL:

• Reversing the doubly linked list is very easy.
• It can allocate or reallocate memory easily during its execution.
• As with a singly linked list, it is the easiest data structure to implement.
• The traversal of this doubly linked list is bidirectional which is not possible in a singly linked list.
• Deletion of nodes is easy as compared to a Singly Linked List. A singly linked list deletion requires a pointer to the node and previous node to be deleted but in the doubly linked list, it only required the pointer which is to be deleted.

Disadvantages Of DLL:

• It uses extra memory when compared to the array and singly linked list.
• Since elements in memory are stored randomly, therefore the elements are accessed sequentially no direct access is allowed.

Uses Of DLL:

• It is used in the navigation systems where front and back navigation is required.
• It is used by the browser to implement backward and forward navigation of visited web pages that is a back and forward button.
• It is also used to represent a classic game deck of cards.
• It is also used by various applications to implement undo and redo functionality.
• Doubly Linked List is also used in constructing MRU/LRU (Most/least recently used) cache.
• Other data structures like stacks, Hash Tables, Binary trees can also be constructed or programmed using a doubly-linked list.
• Also in many operating systems, the thread scheduler(the thing that chooses what process needs to run at which time) maintains a doubly-linked list of all processes running at that time.

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Difference between Singly linked list and Doubly linked list

Introduction to Singly linked list : A singly linked list is a set of nodes where each node has two fields ‘data’ and ‘link’. The ‘data’ field stores actual piece of information and ‘link’ field is used to point to next node. Basically the ‘link’ field stores the address of the next node.

Introduction to Doubly linked list : A Doubly Linked List (DLL) contains an extra pointer, typically called previous pointer, together with next pointer and data which are there in singly linked list.

Singly linked list vs Doubly linked list

Singly linked list (SLL)	Doubly linked list (DLL)
SLL nodes contains 2 field -data field and next link field.	DLL nodes contains 3 fields -data field, a previous link field and a next link field.
In SLL, the traversal can be done using the next node link only. Thus traversal is possible in one direction only.	In DLL, the traversal can be done using the previous node link or the next node link. Thus traversal is possible in both directions (forward and backward).
The SLL occupies less memory than DLL as it has only 2 fields.	The DLL occupies more memory than SLL as it has 3 fields.
Complexity of insertion and deletion at a given position is O(n).	Complexity of insertion and deletion at a given position is O(1).

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Difference Between Doubly linked list vs Singly linked list

• The singly linked list and doubly linked list is a type of linked list to arrange memory and information.
• The singly linked list and doubly linked list is part of dynamic data structure to avoid memory wastage and traverse using element in the list.
• The doubly linked list is a function that contains data, next node, and previous node simultaneously.
• The singly linked list is a function that contains data and the next node only.
• The singly linked list is a simple linked list to traverse one way from the first node to the next node.
• The doubly linked list is a complex linked list to traverse both ways from one node to another and vice versa.
• The singly linked list contains two parts, such as memory and pointer, but the last pointer becomes null.
• The doubly linked list contains three parts such as a previous pointer, memory node, and next pointer but the initial and last pointer becomes null.

Head to Head Comparison Between Doubly linked list vs Singly linked list (Infographics)

Below are the top differences between Doubly linked list vs Singly linked list

Key differences between Doubly linked list vs Singly linked list

Some of the key differences between Doubly linked list vs Singly linked list are given below:

• The doubly linked list is bidirectional because of two address pointer. Therefore, a singly linked list is unidirectional because of the one address pointer.
• The doubly linked list has occurred more memory space than the singly linked list.
• The singly linked list simple, whereas the doubly linked list, is a complex dynamic data structure of the list.
• The doubly linked list provides an empty head and tail pointer. Hence, a singly linked list provides an empty tail only.
• The doubly linked list more efficient than the singly list.
• The doubly linked list contains three parameters, and the singly linked list contains two parameters.
• The singly linked list image is given below.

• The doubly linked list image is given below.

• The doubly linked list gives time complexity O(1), whereas the singly linked list gives time complexity O(n).

Comparison table

• The doubly linked list is a complex function, and the singly linked list is a simple data structure.
• The comparison table is displayed features and descriptions of the singly linked list and doubly linked list.
• The below table is showing similarities and differences of the type of the linked list.

Features	doubly linked list	singly linked list
Definition	The doubly linked list is a complex linked list to manage memory with previous and next pointer.	The singly linked list is a simple linked list to manage memory with the next pointer.
Function	Organize dynamic data structure or values of the list.	Organize dynamic data structure or values of the list.
Parameter	Memory node Previous node Next node	Memory node Next node
Algorithm	The doubly linked list algorithm is below. 1) set Pointer = null 2) set New node = pointer 3) set Pointer = pointer -> next 4) set New node -> data = value 5) set New node -> previous = null 6) set New node -> next = start 7) set New head -> previous = New node 8) set New head = New node (continue procedure until last pointer) 9) last pointer -> null = tail 10) exit	The singly linked list algorithm is below. 1) set Pointer = null 2) set New node = pointer 3) set Pointer = pointer -> next 4) set New node -> data = value 5) set New node -> next = new head 6) set New head = New node (continue procedure until last pointer) 7) last pointer -> null = tail 8) exit
Description	The head pointer and tail are empty. Other nodes are including data.	The tail pointer is empty. The head and other nodes are including data.
direction	The node pointer addresses forward and reverses direction in the linked list. The doubly linked list supports bidirectional.	The node pointer addresses only the forward direction because of the next node. This linked list does not traverse the reverse direction. The doubly linked list supports unidirectional.
Memory space	The doubly linked list contains two addresses of the node. This variable takes 8-byte memory space.	The singly linked list contains one address of the node. This variable takes 4-byte memory spaces.
Time complexity	The time complexity of basic operation such as insert and delete of the list is O (1).	The time complexity of basic operation such as insert and delete of the list is Popular Course in this category Java Training (40 Courses, 29 Projects, 4 Quizzes)40 Online Courses | 29 Hands-on Projects | 285+ Hours | Verifiable Certificate of Completion | Lifetime Access | 4 Quizzes with Solutions 4.8 (12,290 ratings) Course Price View Course Related Courses Python Training Program (39 Courses, 13+ Projects)HTML Training (12 Courses, 19+ Projects, 4 Quizzes) O (n).
complexity	The doubly linked list is complex than a singly linked list to handle and operate data. It is difficult to manage data and its address.	The singly linked list is simple than a doubly-linked list to handle and operate data. It is easy to manage data and its address.
Operation	Insert the data in the list. Delete the data from the list. Traversing from each element Searching element from the linked list	Insert the data in the list. Delete the data from the list. Traversing from each element Searching element from the linked list
Advantages and limitations	Random access to the data is possible. The deletion is easy than the singly linked list. Uses more memory than the singly linked list. Easy to operate and handle any data.	Random access to the data is possible. The insertion process is easy than the doubly linked list. Use less memory. Cannot handle previous data of the list.
Implementation	Stack Hash table Binary tree	Stack Queue Fibonacci heap
Real-time Example	Navigation system to get backward and forward place. Operate Undo and Redo functionality in the application.	The queue of the people. Utensil or plate dispenser in the buffet.

Conclusion

• The singly linked list and doubly linked list make the application usable, handy, and manageable.
• The singly linked list and doubly linked list helps to manage and operate a list of data.

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