G4G0-2/Data Structures/AI Notes/Singly and Doubly linked list.md

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).
Supports lesser number of operations in constant time	Supports additional operations like insert before, delete previous, delete current node and delete last in O(1) time. Since it supports delete last, it is used to efficiently implement Deque.
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 deletion with a given node is O(n), because the previous node needs to be known, and traversal takes O(n)	Complexity of deletion with a given node is O(1) because the previous node can be accessed easily
A singly linked list consumes less memory as compared to the doubly linked list.	The doubly linked list consumes more memory as compared to the singly linked list.
Singly linked list is relatively less used in practice due to limited number of operations	Doubly linked list is implemented more in libraries due to wider number of operations. For example Java LinkedList implements Doubly Linked List.