Linked List | Set 1 (Introduction)

• Difficulty Level : Easy
• Last Updated : 18 Jan, 2022

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. 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 but in Linked list if we have the head node then we can traverse to any node through it and insert new node at the required position.
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 due to this so much work is being done which affects the efficiency of the code.
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(head 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 points to NULL.
Each node in a list consists of at least two parts:
1) data (we can store integer, strings or any type of data).
2) Pointer (Or Reference) to the next node (connects one node to another)
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 nodestruct 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 classclass 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 classclass 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#

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 nodevoid printList(Node* n){    while (n != NULL) {        cout << n->data << " ";        n = n->next;    }} // Driver codeint 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 nodevoid 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;}



Output:

1  2  3