There are various linked list operations that allow us to perform different actions on linked lists. For example, the insertion operation adds a new element to the linked list.
Here's a list of basic linked list operations that we will cover in this article.
- Traversal - access each element of the linked list
- Insertion - adds a new element to the linked list
- Deletion - removes the existing elements
- Search - find a node in the linked list
- Sort - sort the nodes of the linked list
Before you learn about linked list operations in detail, make sure to know about Linked List first.
Things to Remember about Linked List
- head points to the first node of the linked list
- next pointer of the last node is NULL, so if the next current node is NULL, we have reached the end of the linked list.
In all of the examples, we will assume that the linked list has three nodes 1 --->2 --->3 with node structure as below:
struct node { int data; struct node *next; };
Traverse a Linked List :
Displaying the contents of a linked list is very simple. We keep moving the temp node to the next one and display its contents.
When temp is NULL, we know that we have reached the end of the linked list so we get out of the while loop.
struct node *temp = head; printf("\n\nList elements are - \n"); while(temp != NULL) { printf("%d --->",temp->data); temp = temp->next; } --------Output-------- List elements are - 1 --->2 --->3 --->
Insert Elements to a Linked List :
You can add elements to either the beginning, middle or end of the linked list.
1. Insert at the beginning
- Allocate memory for new node
- Store data
- Change next of new node to point to head
- Change head to point to recently created node
struct node *newNode; newNode = malloc(sizeof(struct node)); newNode->data = 4; newNode->next = head; head = newNode;
2. Insert at the End
- Allocate memory for new node
- Store data
- Traverse to last node
- Change next of last node to recently created node
struct node *newNode; newNode = malloc(sizeof(struct node)); newNode->data = 4; newNode->next = NULL; struct node *temp = head; while(temp->next != NULL){ temp = temp->next; } temp->next = newNode;
3. Insert at the Middle
- Allocate memory and store data for new node
- Traverse to node just before the required position of new node
- Change next pointers to include new node in between
struct node *newNode; newNode = malloc(sizeof(struct node)); newNode->data = 4; struct node *temp = head; for(int i=2; i < position; i++) { if(temp->next != NULL) { temp = temp->next; } } newNode->next = temp->next; temp->next = newNode;
Delete from a Linked List :
You can delete either from the beginning, end or from a particular position.
1. Delete from beginning
- Point head to the second node
head = head->next;
2. Delete from end
- Traverse to second last element
- Change its next pointer to null
struct node* temp = head; while(temp->next->next!=NULL){ temp = temp->next; } temp->next = NULL;
3. Delete from middle
- Traverse to element before the element to be deleted
- Change next pointers to exclude the node from the chain
for(int i=2; i< position; i++) {
if(temp->next!=NULL) {
temp = temp->next;
}
}
temp->next = temp->next->next; Search an Element on a Linked List :
You can search an element on a linked list using a loop using the following steps. We are finding item on a linked list.
- Make head as the current node.
- Run a loop until the current node is NULL because the last element points to NULL.
- In each iteration, check if the key of the node is equal to item. If it the key matches the item, return true otherwise return false.
// Search a node bool searchNode(struct Node** head_ref, int key) { struct Node* current = *head_ref; while (current != NULL) { if (current->data == key) return true; current = current->next; } return false; }
Sort Elements of a Linked List :
We will use a simple sorting algorithm, Bubble Sort, to sort the elements of a linked list in ascending order below.
- Make the head as the current node and create another node index for later use.
- If head is null, return.
- Else, run a loop till the last node (i.e. NULL).
- In each iteration, follow the following step 5-6.
- Store the next node of current in index.
- Check if the data of the current node is greater than the next node. If it is greater, swap current and index.
// Sort the linked list void sortLinkedList(struct Node** head_ref) { struct Node *current = *head_ref, *index = NULL; int temp; if (head_ref == NULL) { return; } else { while (current != NULL) { // index points to the node next to current index = current->next; while (index != NULL) { if (current->data > index->data) { temp = current->data; current->data = index->data; index->data = temp; } index = index->next; } current = current->next; } } }
Linked List Operations in C:
// Linked list operations in C
#include <stdio.h>
#include <stdlib.h>
// Create a node
struct Node {
int data;
struct Node* next;
};
// Insert at the beginning
void insertAtBeginning(struct Node** head_ref, int new_data) {
// Allocate memory to a node
struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
// insert the data
new_node->data = new_data;
new_node->next = (*head_ref);
// Move head to new node
(*head_ref) = new_node;
}
// Insert a node after a node
void insertAfter(struct Node* prev_node, int new_data) {
if (prev_node == NULL) {
printf("the given previous node cannot be NULL");
return;
}
struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
new_node->data = new_data;
new_node->next = prev_node->next;
prev_node->next = new_node;
}
// Insert the the end
void insertAtEnd(struct Node** head_ref, int new_data) {
struct Node* new_node = (struct Node*)malloc(sizeof(struct Node));
struct Node* last = *head_ref; /* used in step 5*/
new_node->data = new_data;
new_node->next = NULL;
if (*head_ref == NULL) {
*head_ref = new_node;
return;
}
while (last->next != NULL) last = last->next;
last->next = new_node;
return;
}
// Delete a node
void deleteNode(struct Node** head_ref, int key) {
struct Node *temp = *head_ref, *prev;
if (temp != NULL && temp->data == key) {
*head_ref = temp->next;
free(temp);
return;
}
// Find the key to be deleted
while (temp != NULL && temp->data != key) {
prev = temp;
temp = temp->next;
}
// If the key is not present
if (temp == NULL) return;
// Remove the node
prev->next = temp->next;
free(temp);
}
// Search a node
int searchNode(struct Node** head_ref, int key) {
struct Node* current = *head_ref;
while (current != NULL) {
if (current->data == key) return 1;
current = current->next;
}
return 0;
}
// Sort the linked list
void sortLinkedList(struct Node** head_ref) {
struct Node *current = *head_ref, *index = NULL;
int temp;
if (head_ref == NULL) {
return;
} else {
while (current != NULL) {
// index points to the node next to current
index = current->next;
while (index != NULL) {
if (current->data > index->data) {
temp = current->data;
current->data = index->data;
index->data = temp;
}
index = index->next;
}
current = current->next;
}
}
}
// Print the linked list
void printList(struct Node* node) {
while (node != NULL) {
printf(" %d ", node->data);
node = node->next;
}
}
// Driver program
int main() {
struct Node* head = NULL;
insertAtEnd(&head, 1);
insertAtBeginning(&head, 2);
insertAtBeginning(&head, 3);
insertAtEnd(&head, 4);
insertAfter(head->next, 5);
printf("Linked list: ");
printList(head);
printf("\nAfter deleting an element: ");
deleteNode(&head, 3);
printList(head);
int item_to_find = 3;
if (searchNode(&head, item_to_find)) {
printf("\n%d is found", item_to_find);
} else {
printf("\n%d is not found", item_to_find);
}
sortLinkedList(&head);
printf("\nSorted List: ");
printList(head);
}
Linked List Operations in Java:
// Linked list operations in Java
class LinkedList {
Node head;
// Create a node
class Node {
int data;
Node next;
Node(int d) {
data = d;
next = null;
}
}
// Insert at the beginning
public void insertAtBeginning(int new_data) {
// insert the data
Node new_node = new Node(new_data);
new_node.next = head;
head = new_node;
}
// Insert after a node
public void insertAfter(Node prev_node, int new_data) {
if (prev_node == null) {
System.out.println("The given previous node cannot be null");
return;
}
Node new_node = new Node(new_data);
new_node.next = prev_node.next;
prev_node.next = new_node;
}
// Insert at the end
public void insertAtEnd(int new_data) {
Node new_node = new Node(new_data);
if (head == null) {
head = new Node(new_data);
return;
}
new_node.next = null;
Node last = head;
while (last.next != null)
last = last.next;
last.next = new_node;
return;
}
// Delete a node
void deleteNode(int position) {
if (head == null)
return;
Node temp = head;
if (position == 0) {
head = temp.next;
return;
}
// Find the key to be deleted
for (int i = 0; temp != null && i < position - 1; i++)
temp = temp.next;
// If the key is not present
if (temp == null || temp.next == null)
return;
// Remove the node
Node next = temp.next.next;
temp.next = next;
}
// Search a node
boolean search(Node head, int key) {
Node current = head;
while (current != null) {
if (current.data == key)
return true;
current = current.next;
}
return false;
}
// Sort the linked list
void sortLinkedList(Node head) {
Node current = head;
Node index = null;
int temp;
if (head == null) {
return;
} else {
while (current != null) {
// index points to the node next to current
index = current.next;
while (index != null) {
if (current.data > index.data) {
temp = current.data;
current.data = index.data;
index.data = temp;
}
index = index.next;
}
current = current.next;
}
}
}
// Print the linked list
public void printList() {
Node tnode = head;
while (tnode != null) {
System.out.print(tnode.data + " ");
tnode = tnode.next;
}
}
public static void main(String[] args) {
LinkedList llist = new LinkedList();
llist.insertAtEnd(1);
llist.insertAtBeginning(2);
llist.insertAtBeginning(3);
llist.insertAtEnd(4);
llist.insertAfter(llist.head.next, 5);
System.out.println("Linked list: ");
llist.printList();
System.out.println("\nAfter deleting an element: ");
llist.deleteNode(3);
llist.printList();
System.out.println();
int item_to_find = 3;
if (llist.search(llist.head, item_to_find))
System.out.println(item_to_find + " is found");
else
System.out.println(item_to_find + " is not found");
llist.sortLinkedList(llist.head);
System.out.println("\nSorted List: ");
llist.printList();
}
}
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