# Linked List | Set 1 (Introduction)

• Difficulty Level : Easy
• Last Updated : 10 Nov, 2021

Like arrays, Linked List is a linear data structure. Unlike arrays, linked list elements are not stored at a contiguous location; the elements are linked using pointers. Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

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Arrays can be used to store linear data of similar types, but arrays have the following limitations.
1) The size of the arrays is fixed: So we must know the upper limit on the number of elements in advance. Also, generally, the allocated memory is equal to the upper limit irrespective of the usage.
2) Inserting a new element in an array of elements is expensive because the room has to be created for the new elements and to create room existing elements have to be shifted.
For example, in a system, if we maintain a sorted list of IDs in an array id[].
id[] = [1000, 1010, 1050, 2000, 2040].
And if we want to insert a new ID 1005, then to maintain the sorted order, we have to move all the elements after 1000 (excluding 1000).
Deletion is also expensive with arrays until unless some special techniques are used. For example, to delete 1010 in id[], everything after 1010 has to be moved.
1) Dynamic size
2) Ease of insertion/deletion
Drawbacks:
1) Random access is not allowed. We have to access elements sequentially starting from the first node. So we cannot do binary search with linked lists efficiently with its default implementation. Read about it here
2) Extra memory space for a pointer is required with each element of the list.
3) Not cache friendly. Since array elements are contiguous locations, there is locality of reference which is not there in case of linked lists.
Representation:
A linked list is represented by a pointer to the first node of the linked list. The first node is called the head. If the linked list is empty, then the value of the head is NULL.
Each node in a list consists of at least two parts:
1) data
2) Pointer (Or Reference) to the next node
In C, we can represent a node using structures. Below is an example of a linked list node with integer data.
In Java or C#, LinkedList can be represented as a class and a Node as a separate class. The LinkedList class contains a reference of Node class type.

## C

 `// A linked list node``struct` `Node {``    ``int` `data;``    ``struct` `Node* next;``};`

## C++

 `class` `Node {``public``:``    ``int` `data;``    ``Node* next;``};`

## Java

 `class` `LinkedList {``    ``Node head; ``// head of the list` `    ``/* Linked list Node*/``    ``class` `Node {``        ``int` `data;``        ``Node next;` `        ``// Constructor to create a new node``        ``// Next is by default initialized``        ``// as null``        ``Node(``int` `d) { data = d; }``    ``}``}`

## Python

 `# Node class``class` `Node:`` ` `    ``# Function to initialize the node object``    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data  ``# Assign data``        ``self``.``next` `=` `None`  `# Initialize``                          ``# next as null`` ` `# Linked List class``class` `LinkedList:``   ` `    ``# Function to initialize the Linked``    ``# List object``    ``def` `__init__(``self``):``        ``self``.head ``=` `None`

## C#

 `class` `LinkedList {``    ``// The first node(head) of the linked list``    ``// Will be an object of type Node (null by default)``    ``Node head;` `    ``class` `Node {``        ``int` `data;``        ``Node next;` `        ``// Constructor to create a new node``        ``Node(``int` `d) { data = d; }``    ``}``}`

## Javascript

 ``

First Simple Linked List in C Let us create a simple linked list with 3 nodes.

## C++

 `// A simple CPP program to introduce``// a linked list``#include ``using` `namespace` `std;` `class` `Node {``public``:``    ``int` `data;``    ``Node* next;``};` `// Program to create a simple linked``// list with 3 nodes``int` `main()``{``    ``Node* head = NULL;``    ``Node* second = NULL;``    ``Node* third = NULL;` `    ``// allocate 3 nodes in the heap``    ``head = ``new` `Node();``    ``second = ``new` `Node();``    ``third = ``new` `Node();` `    ``/* Three blocks have been allocated dynamically.``    ``We have pointers to these three blocks as head,``    ``second and third    ``    ``head         second         third``        ``|             |             |``        ``|             |             |``    ``+---+-----+     +----+----+     +----+----+``    ``| # | # |     | # | # |     | # | # |``    ``+---+-----+     +----+----+     +----+----+``    ` `# represents any random value.``Data is random because we haven’t assigned``anything yet */` `    ``head->data = 1; ``// assign data in first node``    ``head->next = second; ``// Link first node with``    ``// the second node` `    ``/* data has been assigned to the data part of first``    ``block (block pointed by the head). And next``    ``pointer of the first block points to second.``    ``So they both are linked.` `    ``head         second         third``        ``|             |             |``        ``|             |             |``    ``+---+---+     +----+----+     +-----+----+``    ``| 1 | o----->| # | # |     | # | # |``    ``+---+---+     +----+----+     +-----+----+    ``*/` `    ``// assign data to second node``    ``second->data = 2;` `    ``// Link second node with the third node``    ``second->next = third;` `    ``/* data has been assigned to the data part of the second``    ``block (block pointed by second). And next``    ``pointer of the second block points to the third``    ``block. So all three blocks are linked.``    ` `    ``head         second         third``        ``|             |             |``        ``|             |             |``    ``+---+---+     +---+---+     +----+----+``    ``| 1 | o----->| 2 | o-----> | # | # |``    ``+---+---+     +---+---+     +----+----+     */` `    ``third->data = 3; ``// assign data to third node``    ``third->next = NULL;` `    ``/* data has been assigned to the data part of the third``    ``block (block pointed by third). And next pointer``    ``of the third block is made NULL to indicate``    ``that the linked list is terminated here.` `    ``We have the linked list ready.` `        ``head    ``            ``|``            ``|``        ``+---+---+     +---+---+     +----+------+``        ``| 1 | o----->| 2 | o-----> | 3 | NULL |``        ``+---+---+     +---+---+     +----+------+    ``    ` `    ` `    ``Note that only the head is sufficient to represent``    ``the whole list. We can traverse the complete``    ``list by following the next pointers. */` `    ``return` `0;``}` `// This code is contributed by rathbhupendra`

## C

 `// A simple C program to introduce``// a linked list``#include ``#include ` `struct` `Node {``    ``int` `data;``    ``struct` `Node* next;``};` `// Program to create a simple linked``// list with 3 nodes``int` `main()``{``    ``struct` `Node* head = NULL;``    ``struct` `Node* second = NULL;``    ``struct` `Node* third = NULL;` `    ``// allocate 3 nodes in the heap``    ``head = (``struct` `Node*)``malloc``(``sizeof``(``struct` `Node));``    ``second = (``struct` `Node*)``malloc``(``sizeof``(``struct` `Node));``    ``third = (``struct` `Node*)``malloc``(``sizeof``(``struct` `Node));` `    ``/* Three blocks have been allocated dynamically.``     ``We have pointers to these three blocks as head,``     ``second and third    ``       ``head           second           third``        ``|                |               |``        ``|                |               |``    ``+---+-----+     +----+----+     +----+----+``    ``| #  | #  |     | #  | #  |     |  # |  # |``    ``+---+-----+     +----+----+     +----+----+``   ` `   ``# represents any random value.``   ``Data is random because we haven’t assigned``   ``anything yet  */` `    ``head->data = 1; ``// assign data in first node``    ``head->next = second; ``// Link first node with``    ``// the second node` `    ``/* data has been assigned to the data part of the first``     ``block (block pointed by the head). And next``     ``pointer of first block points to second. ``     ``So they both are linked.` `       ``head          second         third``        ``|              |              |``        ``|              |              |``    ``+---+---+     +----+----+     +-----+----+``    ``| 1  | o----->| #  | #  |     |  #  | #  |``    ``+---+---+     +----+----+     +-----+----+   ``  ``*/` `    ``// assign data to second node``    ``second->data = 2;` `    ``// Link second node with the third node``    ``second->next = third;` `    ``/* data has been assigned to the data part of the second``     ``block (block pointed by second). And next``     ``pointer of the second block points to the third``     ``block. So all three blocks are linked.``  ` `       ``head         second         third``        ``|             |             |``        ``|             |             |``    ``+---+---+     +---+---+     +----+----+``    ``| 1  | o----->| 2 | o-----> |  # |  # |``    ``+---+---+     +---+---+     +----+----+      */` `    ``third->data = 3; ``// assign data to third node``    ``third->next = NULL;` `    ``/* data has been assigned to data part of third``    ``block (block pointed by third). And next pointer``    ``of the third block is made NULL to indicate``    ``that the linked list is terminated here.` `     ``We have the linked list ready. ` `           ``head   ``             ``|``             ``|``        ``+---+---+     +---+---+       +----+------+``        ``| 1  | o----->|  2  | o-----> |  3 | NULL |``        ``+---+---+     +---+---+       +----+------+      ``   ` `    ` `    ``Note that only head is sufficient to represent``    ``the whole list.  We can traverse the complete``    ``list by following next pointers.    */` `    ``return` `0;``}`

## Java

 `// A simple Java program to introduce a linked list``class` `LinkedList {``    ``Node head; ``// head of list` `    ``/* Linked list Node.  This inner class is made static so that``       ``main() can access it */``    ``static` `class` `Node {``        ``int` `data;``        ``Node next;``        ``Node(``int` `d)``        ``{``            ``data = d;``            ``next = ``null``;``        ``} ``// Constructor``    ``}` `    ``/* method to create a simple linked list with 3 nodes*/``    ``public` `static` `void` `main(String[] args)``    ``{``        ``/* Start with the empty list. */``        ``LinkedList llist = ``new` `LinkedList();` `        ``llist.head = ``new` `Node(``1``);``        ``Node second = ``new` `Node(``2``);``        ``Node third = ``new` `Node(``3``);` `        ``/* Three nodes have been allocated dynamically.``          ``We have references to these three blocks as head, ``          ``second and third` `          ``llist.head        second              third``             ``|                |                  |``             ``|                |                  |``         ``+----+------+     +----+------+     +----+------+``         ``| 1  | null |     | 2  | null |     |  3 | null |``         ``+----+------+     +----+------+     +----+------+ */` `        ``llist.head.next = second; ``// Link first node with the second node` `        ``/*  Now next of the first Node refers to the second.  So they``            ``both are linked.` `         ``llist.head        second              third``            ``|                |                  |``            ``|                |                  |``        ``+----+------+     +----+------+     +----+------+``        ``| 1  |  o-------->| 2  | null |     |  3 | null |``        ``+----+------+     +----+------+     +----+------+ */` `        ``second.next = third; ``// Link second node with the third node` `        ``/*  Now next of the second Node refers to third.  So all three``            ``nodes are linked.` `         ``llist.head        second              third``            ``|                |                  |``            ``|                |                  |``        ``+----+------+     +----+------+     +----+------+``        ``| 1  |  o-------->| 2  |  o-------->|  3 | null |``        ``+----+------+     +----+------+     +----+------+ */``    ``}``}`

## Python

 `# A simple Python program to introduce a linked list` `# Node class``class` `Node:` `    ``# Function to initialise the node object``    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data  ``# Assign data``        ``self``.``next` `=` `None`  `# Initialize next as null`  `# Linked List class contains a Node object``class` `LinkedList:` `    ``# Function to initialize head``    ``def` `__init__(``self``):``        ``self``.head ``=` `None`  `# Code execution starts here``if` `__name__``=``=``'__main__'``:` `    ``# Start with the empty list``    ``llist ``=` `LinkedList()` `    ``llist.head ``=` `Node(``1``)``    ``second ``=` `Node(``2``)``    ``third ``=` `Node(``3``)` `    ``'''``    ``Three nodes have been created.``    ``We have references to these three blocks as head,``    ``second and third` `    ``llist.head        second              third``         ``|                |                  |``         ``|                |                  |``    ``+----+------+     +----+------+     +----+------+``    ``| 1  | None |     | 2  | None |     |  3 | None |``    ``+----+------+     +----+------+     +----+------+``    ``'''` `    ``llist.head.``next` `=` `second; ``# Link first node with second` `    ``'''``    ``Now next of first Node refers to second.  So they``    ``both are linked.` `    ``llist.head        second              third``         ``|                |                  |``         ``|                |                  |``    ``+----+------+     +----+------+     +----+------+``    ``| 1  |  o-------->| 2  | null |     |  3 | null |``    ``+----+------+     +----+------+     +----+------+``    ``'''` `    ``second.``next` `=` `third; ``# Link second node with the third node` `    ``'''``    ``Now next of second Node refers to third.  So all three``    ``nodes are linked.` `    ``llist.head        second              third``         ``|                |                  |``         ``|                |                  |``    ``+----+------+     +----+------+     +----+------+``    ``| 1  |  o-------->| 2  |  o-------->|  3 | null |``    ``+----+------+     +----+------+     +----+------+``    ``'''`

## C#

 `// A simple C# program to introduce a linked list``using` `System;` `public` `class` `LinkedList {``    ``Node head; ``// head of list` `    ``/* Linked list Node. This inner class is made static so that``    ``main() can access it */``    ``public` `class` `Node {``        ``public` `int` `data;``        ``public` `Node next;``        ``public` `Node(``int` `d)``        ``{``            ``data = d;``            ``next = ``null``;``        ``} ``// Constructor``    ``}` `    ``/* method to create a simple linked list with 3 nodes*/``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``/* Start with the empty list. */``        ``LinkedList llist = ``new` `LinkedList();` `        ``llist.head = ``new` `Node(1);``        ``Node second = ``new` `Node(2);``        ``Node third = ``new` `Node(3);` `        ``/* Three nodes have been allocated dynamically.``        ``We have references to these three blocks as head,``        ``second and third` `        ``llist.head     second             third``            ``|             |                 |``            ``|             |                 |``        ``+----+------+     +----+------+     +----+------+``        ``| 1 | null |     | 2 | null |     | 3 | null |``        ``+----+------+     +----+------+     +----+------+ */` `        ``llist.head.next = second; ``// Link first node with the second node` `        ``/* Now next of first Node refers to second. So they``            ``both are linked.` `        ``llist.head     second             third``            ``|             |                 |``            ``|             |                 |``        ``+----+------+     +----+------+     +----+------+``        ``| 1 | o-------->| 2 | null |     | 3 | null |``        ``+----+------+     +----+------+     +----+------+ */` `        ``second.next = third; ``// Link second node with the third node` `        ``/* Now next of the second Node refers to third. So all three``            ``nodes are linked.` `        ``llist.head     second             third``            ``|             |                 |``            ``|             |                 |``        ``+----+------+     +----+------+     +----+------+``        ``| 1 | o-------->| 2 | o-------->| 3 | null |``        ``+----+------+     +----+------+     +----+------+ */``    ``}``}` `// This code has been contributed by 29AjayKumar`

In the previous program, we have created a simple linked list with three nodes. Let us traverse the created list and print the data of each node. For traversal, let us write a general-purpose function printList() that prints any given list.

## C++

 `// A simple C++ program for traversal of a linked list``#include ``using` `namespace` `std;` `class` `Node {``public``:``    ``int` `data;``    ``Node* next;``};` `// This function prints contents of linked list``// starting from the given node``void` `printList(Node* n)``{``    ``while` `(n != NULL) {``        ``cout << n->data << ``" "``;``        ``n = n->next;``    ``}``}` `// Driver code``int` `main()``{``    ``Node* head = NULL;``    ``Node* second = NULL;``    ``Node* third = NULL;` `    ``// allocate 3 nodes in the heap``    ``head = ``new` `Node();``    ``second = ``new` `Node();``    ``third = ``new` `Node();` `    ``head->data = 1; ``// assign data in first node``    ``head->next = second; ``// Link first node with second` `    ``second->data = 2; ``// assign data to second node``    ``second->next = third;` `    ``third->data = 3; ``// assign data to third node``    ``third->next = NULL;` `    ``printList(head);` `    ``return` `0;``}` `// This is code is contributed by rathbhupendra`

## C

 `// A simple C program for traversal of a linked list``#include ``#include ` `struct` `Node {``    ``int` `data;``    ``struct` `Node* next;``};` `// This function prints contents of linked list starting from``// the given node``void` `printList(``struct` `Node* n)``{``    ``while` `(n != NULL) {``        ``printf``(``" %d "``, n->data);``        ``n = n->next;``    ``}``}` `int` `main()``{``    ``struct` `Node* head = NULL;``    ``struct` `Node* second = NULL;``    ``struct` `Node* third = NULL;` `    ``// allocate 3 nodes in the heap``    ``head = (``struct` `Node*)``malloc``(``sizeof``(``struct` `Node));``    ``second = (``struct` `Node*)``malloc``(``sizeof``(``struct` `Node));``    ``third = (``struct` `Node*)``malloc``(``sizeof``(``struct` `Node));` `    ``head->data = 1; ``// assign data in first node``    ``head->next = second; ``// Link first node with second` `    ``second->data = 2; ``// assign data to second node``    ``second->next = third;` `    ``third->data = 3; ``// assign data to third node``    ``third->next = NULL;` `    ``printList(head);` `    ``return` `0;``}`

## Java

 `// A simple Java program for traversal of a linked list``class` `LinkedList {``    ``Node head; ``// head of list` `    ``/* Linked list Node.  This inner class is made static so that``       ``main() can access it */``    ``static` `class` `Node {``        ``int` `data;``        ``Node next;``        ``Node(``int` `d)``        ``{``            ``this``.data = d;``            ``next = ``null``;``        ``} ``// Constructor``    ``}` `    ``/* This function prints contents of linked list starting from head */``    ``public` `void` `printList()``    ``{``        ``Node n = head;``        ``while` `(n != ``null``) {``            ``System.out.print(n.data + ``" "``);``            ``n = n.next;``        ``}``    ``}` `    ``/* method to create a simple linked list with 3 nodes*/``    ``public` `static` `void` `main(String[] args)``    ``{``        ``/* Start with the empty list. */``        ``LinkedList llist = ``new` `LinkedList();` `        ``llist.head = ``new` `Node(``1``);``        ``Node second = ``new` `Node(``2``);``        ``Node third = ``new` `Node(``3``);` `        ``llist.head.next = second; ``// Link first node with the second node``        ``second.next = third; ``// Link second node with the third node` `        ``llist.printList();``    ``}``}`

## Python3

 `# A simple Python program for traversal of a linked list` `# Node class``class` `Node:` `    ``# Function to initialise the node object``    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data  ``# Assign data``        ``self``.``next` `=` `None`  `# Initialize next as null`  `# Linked List class contains a Node object``class` `LinkedList:` `    ``# Function to initialize head``    ``def` `__init__(``self``):``        ``self``.head ``=` `None` `    ``# This function prints contents of linked list``    ``# starting from head``    ``def` `printList(``self``):``        ``temp ``=` `self``.head``        ``while` `(temp):``            ``print` `(temp.data)``            ``temp ``=` `temp.``next`  `# Code execution starts here``if` `__name__``=``=``'__main__'``:` `    ``# Start with the empty list``    ``llist ``=` `LinkedList()` `    ``llist.head ``=` `Node(``1``)``    ``second ``=` `Node(``2``)``    ``third ``=` `Node(``3``)` `    ``llist.head.``next` `=` `second; ``# Link first node with second``    ``second.``next` `=` `third; ``# Link second node with the third node` `    ``llist.printList()`

## C#

 `// A simple C# program for traversal of a linked list``using` `System;` `public` `class` `LinkedList {``    ``Node head; ``// head of list` `    ``/* Linked list Node. This inner``    ``class is made static so that``    ``main() can access it */``    ``public` `class` `Node {``        ``public` `int` `data;``        ``public` `Node next;``        ``public` `Node(``int` `d)``        ``{``            ``data = d;``            ``next = ``null``;` `        ``} ``// Constructor``    ``}` `    ``/* This function prints contents of``    ``linked list starting from head */``    ``public` `void` `printList()``    ``{``        ``Node n = head;``        ``while` `(n != ``null``) {``            ``Console.Write(n.data + ``" "``);``            ``n = n.next;``        ``}``    ``}` `    ``/* method to create a simple linked list with 3 nodes*/``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``/* Start with the empty list. */``        ``LinkedList llist = ``new` `LinkedList();` `        ``llist.head = ``new` `Node(1);``        ``Node second = ``new` `Node(2);``        ``Node third = ``new` `Node(3);` `        ``llist.head.next = second; ``// Link first node with the second node``        ``second.next = third; ``// Link second node with the third node` `        ``llist.printList();``    ``}``}` `/* This code contributed by PrinciRaj1992 */`

## Javascript

 ``

Output:

` 1  2  3`