Insertion in Singly Linked List

   Last Updated: 06 October, 2024       🕓  7 Mins Read

In this Linked List tutorial, we will see all about the insert operation in a single linked list. In the insert operation, we will add a new node to the linked list at any position.

In a Singly Linked List, we can insert a node at the following positions:

1. At the beginning of the linked list.

2. At a specific position of the linked list.

3. After a given node of the linked list.

4. At the end of the linked list.

1. Insert a node at the beginning of the linked list.

To insert a new node at the beginning or front position in the linked list, follow these steps:

• Create a newNode with given value.

• Check whether list is Empty (head == NULL).

• If list is Empty then, set newNode→next = NULL and head = newNode.

• If list is Not Empty then, set newNode→next = head and head = newNode.

In the below given example we will see how to insert a new node in the beginning or front the linked list.

// Java Program to insert a new node at the beginning of Linked List public class InsertNodeAtBeginningInSLL { // method to insert a new node at the beginning of the linked list static Node insertAtFront(Node head, int data) { // Create a node with the given parameter data Node node = new Node(data); // Assigning next node reference from the head node.next = head; // Return the new node as the new head of the list return node; } // method to print linked list public static void printLinkedList(Node head) { Node tempNode = head; while (tempNode != null) { System.out.print(" " + tempNode.data); tempNode = tempNode.next; } System.out.println(); // Line break } public static void main(String[] args) { // create a head node Node head = new Node(40); head.next = new Node(60); head.next.next = new Node(80); head.next.next.next = new Node(100); // Print the current listed list data System.out.println("Linked List values: "); printLinkedList(head); // Insert a new node at the beginning of the linked list System.out.println("After inserting a Node at the beginning:"); head = insertAtFront(head, 20); // Inserting 20 at the beginning // Print the linked list after inserting a new node at the beginning printLinkedList(head); } }

Output

Linked List values:
40 60 80 100
After inserting a Node at the beginning:
20 40 60 80 100

2. Insert a node at a specific position of the linked list

To insert a new node at the specific position of the linked list, we need to follow the given steps.

• Create a newNode with given value.

• Check whether list is Empty (head == NULL).

• If list is Empty then, set newNode → next = NULL and head = newNode.

• If list is Not Empty then, define a node pointer temp and initialize with head.

• Keep moving the temp to its next node until it reaches to the node after which we want to insert the newNode (until temp1 → data is equal to location, here location is the node value after which we want to insert the newNode).

• Every time check whether temp is reached to last node or not. If it is reached to last node then display 'Given node is not found in the list!!! Insertion not possible!!!' and terminate the function. Otherwise move the temp to next node.

• Finally, Set 'newNode → next = temp → next' and 'temp → next = newNode'

In the below given example we will see how to insert a new node in the specific position in the linked list.

// Java Program to Insert a Node At a Specific Position in Linked List public class InsertNodeAtSpecificPositionInSLL { // Method to insert a new node at the specific position in // the linked list static Node insertAtSpecPosition(Node head, int position, int data) { // Create a node Node node = new Node(data); // If the position is at the beginning means 1 if (position == 1) { node.next = head; head = node; return head; } // If the position is other than 1 Node current = head; for (int i = 1; i < position - 1 && current != null; ++i) { current = current.next; } // If the position is out of bounds if (current == null) { System.out.println("ERROR: Position is out of bounds."); return head; } node.next = current.next; current.next = node; return head; } // Print a linked list static void printLinkedList(Node head) { while (head != null) { System.out.print(" " + head.data); head = head.next; } System.out.println(); // New Line } public static void main(String[] args) { Node head = new Node(10); head.next = new Node(20); head.next.next = new Node(40); head.next.next.next = new Node(50); System.out.print("Linked list before inserting a new node:\n"); printLinkedList(head); // Insert a new node with data 30 at position 3 int data = 30, position = 3; head = insertAtSpecPosition(head, position, data); System.out.print("\nLinked list after inserting 30 at the position " + position + ":\n"); printLinkedList(head); } }

Output

Linked list before inserting a new node:
10 20 40 50

Linked list after inserting 30 at the position 3:
10 20 30 40 50

3. Insert a node after a given node of the linked list.

To insert a new node after a given node in the linked list, we need to follow the given steps.

• Create a newNode with given value.

• Check whether list is Empty (head == NULL).

• If list is Empty then, set newNode → next = NULL and head = newNode.

• If list is Not Empty then, define a node pointer temp and initialize with head.

• Keep moving the temp to its next node until it reaches to the node after which we want to insert the newNode (until temp1 → data is equal to location, here location is the node value after which we want to insert the newNode).

• Every time check whether temp is reached to last node or not. If it is reached to last node then display 'Given node is not found in the list!!! Insertion not possible!!!' and terminate the function. Otherwise move the temp to next node.

• Finally, Set 'newNode → next = temp → next' and 'temp → next = newNode'

In the below given example we will see how to insert a new node after the given node in the linked list.

// Java Program to Insert a Node after a Given Node in Linked List public class InsertNodeAtAfterGivenNodeInSLL { // Method to insert a new Node after a given Node static Node insertAfter(Node head, int key, int new_date) { Node node = head; // Iterate a list and find out the key while (node != null) { if (node.data == key) break; node = node.next; } // if node becomes null means, given key is not // found in linked list if (node == null) return head; // Create a new node with the given data and point // the next of newNode to node's next & // point current next to newNode Node newNode = new Node(new_date); newNode.next = node.next; node.next = newNode; return head; } static void printLinkedList(Node Node) { while (Node != null) { System.out.print(Node.data + " "); Node = Node.next; } System.out.println(); // New Line } public static void main(String[] args) { Node head = new Node(10); head.next = new Node(20); head.next.next = new Node(40); head.next.next.next = new Node(50); System.out.println("Linked List data: "); printLinkedList(head); int key = 20, new_date = 30; // Insert a new node 30, after the node 20 head = insertAfter(head, key, new_date); System.out.println("After insertion, Linked List data: "); printLinkedList(head); } }

Output

Linked List data:
10 20 40 50
After insertion, Linked List data:
10 20 30 40 50

4. Insert a node at the end of the linked list.

To insert a new node at the end or last position in the linked list, follow these steps:

• Create a newNode with given value and newNode → next as NULL.

• Check whether list is Empty (head == NULL).

• If list is Empty then, set head = newNode.

• If list is Not Empty then, define a node pointer temp and initialize with head.

• Keep moving the temp to its next node until it reaches to the last node in the list (until temp → next is equal to NULL).

• Set temp → next = newNode.

In the below given example we will see how to insert a new node at the end of the linked list.

// Java Program to Insert a Node at the End of Linked List public class InsertNodeAtEndInSLL { // Method to insert a new node at the end of the linked list static Node insertAtEnd(Node head, int data) { // Create a new node Node node = new Node(data); // If the Linked List is empty, make the new // node as the head and return if (head == null) { return node; } // Store the head reference in a temporary variable Node last = head; // Traverse till the last node of the linked list while (last.next != null) { last = last.next; } // Change the next pointer of the last node to point to the new node last.next = node; // Return the head of the list return head; } // Method to print linked list static void printLinkedList(Node node) { while (node != null) { System.out.print(" " + node.data); node = node.next; } } public static void main(String[] args) { // Create a linked list Node head = new Node(10); head.next = new Node(20); head.next.next = new Node(30); head.next.next.next = new Node(40); System.out.print("Linked list values: "); printLinkedList(head); // Inserting a node at the end of the linked list head = insertAtEnd(head, 50); System.out.print("\nLinked List values, after inserting at the end: "); printLinkedList(head); } }

Output

Linked list values: 10 20 30 40
Linked List values, after inserting at the end: 10 20 30 40 50