Insert a node at a specific position in a linked list

Last Updated : 03 Apr, 2025

Given a singly linked list, a position pos, and data, the task is to insert that data into a linked list at the given position.

Examples:

Input: 3->5->8->10, data = 2, pos = 2
Output: 3->2->5->8->10

Input: 3->5->8->10, data = 11, pos = 5
Output: 3->5->8->10->11

Insertion-at-a-Specific-Position-of-the-Singly-Linked-List-copy

Insertion at specific position in Linked List

[Expected Approach] Using Iterative Method – O(n) time and O(1) space:

Initialize a variable , say curr points to head and allocate the memory to the new node with the given data.
Traverse the Linked list using curr pointer upto position-1 nodes.
If curr’s next is not null , then next pointer of the new node points to the next of curr node.
The next pointer of current node points to the new node.
return the head of linked list.

Below is the implementation of the above approach:

C++

// C++ program for insertion in a single linked // list at a specified position #include <bits/stdc++.h> using namespace std;  class Node {   public:     int data;     Node *next;     Node(int x) {         data = x;         next = nullptr;     } };  // function to insert a Node at required position Node *insertPos(Node *head, int pos, int data) {      // This condition to check whether the     // position given is valid or not.     if (pos < 1)         return head;      // head will change if pos=1     if (pos == 1) {         Node *newNode = new Node(data);         newNode->next = head;         return newNode;     }      Node *curr = head;      // Traverse to the node that will be     // present just before the new node     for (int i = 1; i < pos - 1 && curr != nullptr; i++) {         curr = curr->next;     }          // If position is greater than the      // number of nodes     if (curr == nullptr)          return head;              Node *newNode = new Node(data);      // update the next pointers     newNode->next = curr->next;     curr->next = newNode;      return head; }  void printList(struct Node *head) {     Node *curr = head;     while (curr != nullptr) {         cout << curr->data << " ";         curr = curr->next;     }     cout << endl; }  int main() {      // Creating the list 3->5->8->10     Node *head = new Node(3);     head->next = new Node(5);     head->next->next = new Node(8);     head->next->next->next = new Node(10);      int data = 12, pos = 3;     head = insertPos(head, pos, data);     printList(head);      return 0; }

// C program for insertion in a single linked // list at a specified position #include <stdio.h> #include <stdlib.h>  struct Node {     int data;     struct Node *next; };  struct Node *createNode(int x);  // Function to insert a Node at the required position struct Node *insertPos(struct Node *head, int pos, int data) {      // return if invalid input     if (pos < 1)         return head;      // Head will change if pos=1     if (pos == 1) {         struct Node *newNode = createNode(data);         newNode->next = head;         return newNode;     }      struct Node *curr = head;      // Traverse to the node that will be     // present just before the new node     for (int i = 1; i < pos - 1 && curr != NULL; i++) {         curr = curr->next;     }          // if position is greater than     // number of nodes     if (curr == NULL)          return head;              struct Node *newNode = createNode(data);      // Update the next pointers     newNode->next = curr->next;     curr->next = newNode;      return head; }  void printList(struct Node *head) {     struct Node *curr = head;     while (curr != NULL) {         printf("%d ", curr->data);         curr = curr->next;     }     printf("\n"); }  struct Node *createNode(int x) {     struct Node *new_node =        (struct Node *)malloc(sizeof(struct Node));     new_node->data = x;     new_node->next = NULL;     return new_node; }  int main() {      // Creating the list 3->5->8->10     struct Node *head = createNode(3);     head->next = createNode(5);     head->next->next = createNode(8);     head->next->next->next = createNode(10);      int data = 12, pos = 3;     head = insertPos(head, pos, data);     printList(head);      return 0; }

Java

// Java program for insertion in a single linked // list at a specified position class Node {     int data;     Node next;      Node(int x) {         data = x;         next = null;     } }  class GfG {      // function to insert a Node at required position     static Node insertPos(Node head, int pos, int data) {          // This condition to check whether the         // position given is valid or not.         if (pos < 1)             return head;          // head will change if pos=1         if (pos == 1) {             Node newNode = new Node(data);             newNode.next = head;             return newNode;         }          Node curr = head;          // Traverse to the node that will be          // present just before the new node         for (int i = 1; i < pos - 1 && curr != null; i++) {             curr = curr.next;         }                  // if position is greater than number of elements         if (curr == null)             return head;                  Node newNode = new Node(data);          // update the next pointers         newNode.next = curr.next;         curr.next = newNode;          return head;     }      static void printList(Node node) {         while (node != null) {             System.out.print(node.data + " ");             node = node.next;         }         System.out.println();     }      public static void main(String[] args) {          // Creating the list 3->5->8->10         Node head = new Node(3);         head.next = new Node(5);         head.next.next = new Node(8);         head.next.next.next = new Node(10);          int data = 12, pos = 3;         head = insertPos(head, pos, data);         printList(head);     } }

Python

# Python program for insertion in a single linked # list at a specified position  class Node:     def __init__(self, x):         self.data = x         self.next = None  # function to insert a Node at required position def insert_pos(head, pos, data):          # This condition to check whether the     # position given is valid or not.     if pos < 1:         return head          # head will change if pos=1     if pos == 1:         new_node = Node(data)         new_node.next = head         return new_node          curr = head          # Traverse to the node that will be      # present just before the new node     for _ in range(1, pos - 1):         if curr == None:             break         curr = curr.next              # if position is greater     # number of nodes     if curr is None:         return head          new_node = Node(data)          # update the next pointers     new_node.next = curr.next     curr.next = new_node          return head      def print_list(head):     curr = head     while curr is not None:         print(curr.data, end=" ")         curr = curr.next     print()  if __name__ == "__main__":          # Creating the list 3->5->8->10     head = Node(3)     head.next = Node(5)     head.next.next = Node(8)     head.next.next.next = Node(10)      data = 12     pos = 3     head = insert_pos(head, pos, data)     print_list(head)

// C# program for insertion in a single linked // list at a specified position using System;  class Node {     public int data;     public Node next;      public Node(int x) {         data = x;         next = null;     } }  class GfG {      // function to insert a Node at required position     static Node InsertPos(Node head, int pos, int data) {          // This condition to check whether the         // position given is valid or not.         if (pos < 1)             return head;          // head will change if pos=1         if (pos == 1) {             Node newHead = new Node(data);             newHead.next = head;             return newHead;         }          Node curr = head;          // Traverse to the node that will be          // present just before the new node         for (int i = 1; i < pos - 1 && curr != null; i++) {             curr = curr.next;         }                  // if position is greater than         // size of list         if (curr == null)             return head;                  Node newNode = new Node(data);          // update the next pointers         newNode.next = curr.next;         curr.next = newNode;          return head;     }      static void PrintList(Node head) {         Node curr = head;         while (curr != null) {             Console.Write(curr.data + " ");             curr = curr.next;         }         Console.WriteLine();     }      static void Main() {          // Creating the list 3->5->8->10         Node head = new Node(3);         head.next = new Node(5);         head.next.next = new Node(8);         head.next.next.next = new Node(10);          int data = 12, pos = 3;         head = InsertPos(head, pos, data);         PrintList(head);     } }

JavaScript

// JavaScript program for insertion in a single linked // list at a specified position  class Node {     constructor(x) {         this.data = x;         this.next = null;     } }  // function to insert a Node at required position function insertPos(head, pos, data) {          // This condition to check whether the     // position given is valid or not.     if (pos < 1)         return head;          // head will change if pos=1     if (pos === 1) {         let newNode = new Node(data);         newNode.next = head;         return newNode;     }          let curr = head;          // Traverse to the node that will be      // present just before the new node     for (let i = 1; i < pos - 1 && curr != null; i++) {         curr = curr.next;     }          // if position is greater     // than size of list     if (curr == null)         return head;              let newNode = new Node(data);          // update the next pointers     newNode.next = curr.next;     curr.next = newNode;          return head; }  function printList(head) {     let curr = head;     while (curr !== null) {         console.log(curr.data);         curr = curr.next;     } }  // Creating the list 3->5->8->10 let head = new Node(3); head.next = new Node(5); head.next.next = new Node(8); head.next.next.next = new Node(10);  let data = 12, pos = 3; head = insertPos(head, pos, data); printList(head);