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Linked List Operations: Traverse, Insert and Delete

In this tutorial, you will learn different operations on a linked list. Also, you will find implementation of linked list operations in C/C++, Python and Java.

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;
}

The output of this program will be:

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;

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.

  1. Make the head as the current node and create another node index for later use.
  2. If head is null, return.
  3. Else, run a loop till the last node (i.e. NULL).
  4. In each iteration, follow the following step 5-6.
  5. Store the next node of current in index.
  6. Check if the data of the current node is greater than the next node. If it is greater, swap current and index.

Check the article on bubble sort for better understanding of its working.

// 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;
    }
  }
}

LinkedList Operations in Python, Java, C, and C++

# Linked list operations in Python


# Create a node
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None


class LinkedList:

    def __init__(self):
        self.head = None

    # Insert at the beginning
    def insertAtBeginning(self, new_data):
        new_node = Node(new_data)

        new_node.next = self.head
        self.head = new_node

    # Insert after a node
    def insertAfter(self, prev_node, new_data):

        if prev_node is None:
            print("The given previous node must inLinkedList.")
            return

        new_node = Node(new_data)
        new_node.next = prev_node.next
        prev_node.next = new_node

    # Insert at the end
    def insertAtEnd(self, new_data):
        new_node = Node(new_data)

        if self.head is None:
            self.head = new_node
            return

        last = self.head
        while (last.next):
            last = last.next

        last.next = new_node

    # Deleting a node
    def deleteNode(self, position):

        if self.head is None:
            return

        temp = self.head

        if position == 0:
            self.head = temp.next
            temp = None
            return

        # Find the key to be deleted
        for i in range(position - 1):
            temp = temp.next
            if temp is None:
                break

        # If the key is not present
        if temp is None:
            return

        if temp.next is None:
            return

        next = temp.next.next

        temp.next = None

        temp.next = next

    # Search an element
    def search(self, key):

        current = self.head

        while current is not None:
            if current.data == key:
                return True

            current = current.next

        return False

    # Sort the linked list
    def sortLinkedList(self, head):
        current = head
        index = Node(None)

        if head is None:
            return
        else:
            while current is not None:
                # index points to the node next to current
                index = current.next

                while index is not None:
                    if current.data > index.data:
                        current.data, index.data = index.data, current.data

                    index = index.next
                current = current.next

    # Print the linked list
    def printList(self):
        temp = self.head
        while (temp):
            print(str(temp.data) + " ", end="")
            temp = temp.next


if __name__ == '__main__':

    llist = LinkedList()
    llist.insertAtEnd(1)
    llist.insertAtBeginning(2)
    llist.insertAtBeginning(3)
    llist.insertAtEnd(4)
    llist.insertAfter(llist.head.next, 5)

    print('linked list:')
    llist.printList()

    print("\nAfter deleting an element:")
    llist.deleteNode(3)
    llist.printList()

    print()
    item_to_find = 3
    if llist.search(item_to_find):
        print(str(item_to_find) + " is found")
    else:
        print(str(item_to_find) + " is not found")

    llist.sortLinkedList(llist.head)
    print("Sorted List: ")
    llist.printList()
// 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();
  }
}
// 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 C++

#include <stdlib.h>

#include <iostream>
using namespace std;

// Create a node
struct Node {
  int data;
  struct Node* next;
};

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) {
  cout << "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 at 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
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 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) {
  cout << 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);

  cout << "Linked list: ";
  printList(head);

  cout << "\nAfter deleting an element: ";
  deleteNode(&head, 3);
  printList(head);

  int item_to_find = 3;
  if (searchNode(&head, item_to_find)) {
  cout << endl << item_to_find << " is found";
  } else {
  cout << endl << item_to_find << " is not found";
  }

  sortLinkedList(&head);
  cout << "\nSorted List: ";
  printList(head);
}
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