A linked list is a linear data structure that consists of a sequence of nodes, where each node contains data and a reference to the next node in the sequence. Unlike arrays, which have a fixed size, linked lists can grow or shrink dynamically as elements are added or removed.
In JavaScript, a linked list can be implemented using objects and references. Each node in the linked list is an object with two properties: value and next. The value property stores the actual value of the node, while the next property is a reference to the next node in the list. The last node in the list has a next value of null.
Types Of LinkedList
There are several types of linked lists, each with its own characteristics and advantages. The most common types of linked lists are:
Singly Linked List: In a singly linked list, each node contains a data element and a reference to the next node in the list. The last node in the list has a reference to null. Singly linked lists are easy to implement and can be used to represent dynamic sets, queues, and stacks. However, they are not efficient for certain operations, such as searching for an element in the list.
Doubly Linked List: In a doubly linked list, each node contains a data element and references to the next and previous nodes in the list. The first node in the list has a null reference for the previous node, and the last node has a null reference for the next node. Doubly linked lists can be traversed in both directions, which makes them useful for certain operations, such as removing an element from the middle of the list.
Circular Linked List: In a circular linked list, the last node in the list has a reference to the first node, creating a circular structure. Circular linked lists can be used to implement circular buffers and other data structures that require a circular order.
Sorted Linked List: A sorted linked list is a singly or doubly linked list in which the nodes are arranged in a sorted order. Inserting a new node requires finding the correct position in the list based on the order of the data elements. Sorted linked lists are useful for maintaining a sorted collection of elements and for certain types of searching and merging operations.
Skip List: A skip list is a type of linked list that allows for faster searching of elements by creating additional references to elements that are further away in the list. Each node in a skip list contains a forward reference to another node in the list, with the probability of the reference being made dependent on a random process. Skip lists can be used to implement sets and maps with faster search times than a typical linked list.
Each type of linked list has its own trade-offs and advantages, and the choice of which to use depends on the specific needs of the application.
Basic Operations in Linked List
There are several basic operations that can be performed on a linked list:
Insertion - adding a new node to the list
Insert at beginning: add a new node at the head of the list
Insert at end: add a new node at the tail of the list
Insert at specific position: add a new node at a given position in the list
Deletion - removing a node from the list
Delete at beginning: remove the node at the head of the list
Delete at end: remove the node at the tail of the list
Delete at specific position: remove the node at a given position in the list
Traversal - visiting all nodes in the list in a specific order
Forward traversal: visit all nodes from head to tail
Reverse traversal: visit all nodes from tail to head
Search - finding a node with a specific value in the list
Update - changing the value of a node in the list
These operations can be implemented differently depending on the type of linked list and the programming language being used. However, the general idea is to manipulate the pointers or references of the nodes in order to achieve the desired behavior.
Linked List Representation
Singly Linked List:
+------+ +------+ +------+ +------+ head | data | -> | data | -> | data | -> | data | -> null +------+ +------+ +------+ +------+Doubly Linked List:
null <-> +------+ <-> +------+ <-> +------+ <-> null | data | <--> | data | <--> | data | +------+ <-> +------+ <-> +------+Circular Linked List:
+------+ +------+ +------+ head | data | -> | data | -> | data | +------+ | | | | ^ | v | v | | +----|----+ | +--------+-----------+----+Singly Linked List with Head and Tail Pointers:
+------+ +------+ +------+ +------+ +------+ head | data | -> | data | -> | data | -> | data | -> | data | -> null +------+ +------+ +------+ +------+ +------+ ^ | tailDoubly Linked List with Head and Tail Pointers:
null <-> +------+ <-> +------+ <-> +------+ <-> +------+ <-> null | data | <--> | data | <--> | data | <--> | data | <--> | data | +------+ <-> +------+ <-> +------+ <-> +------+ <-> ^ | head
These representations show the basic structure of each type of linked list, including the pointers or references that link the nodes together.
Summarizing Up
A linked list is a linear data structure that consists of nodes, each containing a data element and a reference to the next node in the list. It is a dynamic data structure that can grow or shrink in size during program execution. Linked lists provide constant time insertion and deletion operations compared to arrays which have O(n) time complexity. However, traversal of a linked list can be slower than an array since it has to follow each node's reference to get to the desired element. Linked lists are used in a variety of applications such as implementing stacks, queues, and graphs.