Insertion in a Doubly Linked List (DLL)

                                Insertion in a Doubly Linked List (DLL)


A Doubly Linked List (DLL) is a linked list where each node has two pointers:

  • prev → Points to the previous node.
  • next → Points to the next node.

Types of Insertions in DLL

1️⃣ Insert at the Beginning
2️⃣ Insert at the End
3️⃣ Insert at a Specific Position


1️⃣ Insert at the Beginning

Steps:

  1. Create a new node.
  2. Set newNode.next = head (point new node to old head).
  3. Set head.prev = newNode (update old head's previous).
  4. Update head = newNode.

Code:

class DoublyLinkedList {
    class Node {
        int data;
        Node prev, next;
        Node(int data) {
            this.data = data;
            this.prev = this.next = null;
        }
    }

    Node head; // Head of DLL

    void insertAtBeginning(int data) {
        Node newNode = new Node(data);
        if (head != null) {
            newNode.next = head;
            head.prev = newNode;
        }
        head = newNode; // Update head
    }

    void display() {
        Node temp = head;
        while (temp != null) {
            System.out.print(temp.data + " ⇄ ");
            temp = temp.next;
        }
        System.out.println("null");
    }

    public static void main(String[] args) {
        DoublyLinkedList dll = new DoublyLinkedList();
        dll.insertAtBeginning(10);
        dll.insertAtBeginning(20);
        dll.insertAtBeginning(30);
        dll.display();  // Output: 30 ⇄ 20 ⇄ 10 ⇄ null
    }
}

2️⃣ Insert at the End

Steps:

  1. Create a new node.
  2. Traverse to the last node.
  3. Update last.next = newNode.
  4. Set newNode.prev = last.
void insertAtEnd(int data) {
    Node newNode = new Node(data);
    if (head == null) {
        head = newNode;
        return;
    }
    Node temp = head;
    while (temp.next != null) {
        temp = temp.next;
    }
    temp.next = newNode;
    newNode.prev = temp;
}


3️⃣ Insert at a Specific Position

Steps:

  1. Traverse to position pos-1.
  2. Insert new node between prevNode and nextNode.
  3. Update all pointers.

Code:


void insertAtPosition(int data, int pos) {
    Node newNode = new Node(data);
    if (pos == 1) {
        insertAtBeginning(data);
        return;
    }

    Node temp = head;
    for (int i = 1; temp != null && i < pos - 1; i++) {
        temp = temp.next;
    }
    
    if (temp == null) return; // Position out of bounds

    newNode.next = temp.next;
    if (temp.next != null) {
        temp.next.prev = newNode;
    }
    temp.next = newNode;
    newNode.prev = temp;
}

Example Execution

DoublyLinkedList dll = new DoublyLinkedList();
dll.insertAtEnd(10);
dll.insertAtEnd(20);
dll.insertAtEnd(30);
dll.insertAtPosition(25, 3);
dll.display(); // Output: 10 ⇄ 20 ⇄ 25 ⇄ 30 ⇄ null

Comments

Post a Comment

Popular posts from this blog

Two Sum II - Input Array Is Sorted

 Given a 1-indexed array of integers numbers that is already sorted in non-decreasing order , find two numbers such that they add up to a specific target number. Let these two numbers be numbers[index1] and numbers[index2] where 1 <= index1 < index2 <= numbers.length. Return the indices of the two numbers, index1 and index2, added by one as an integer array [index1, index2] of length 2. The tests are generated such that there is exactly one solution. You may not use the same element twice. Your solution must use only constant extra space .   Example 1: Input: numbers = [2,7,11,15], target = 9 Output: [1,2] Explanation: The sum of 2 and 7 is 9. Therefore, index1 = 1, index2 = 2. We return [1, 2]. Example 2: Input: numbers = [2,3,4], target = 6 Output: [1,3] Explanation: The sum of 2 and 4 is 6. Therefore index1 = 1, index2 = 3. We return [1, 3]. Example 3: Input: numbers = [-1,0], target = -1 Output: [1,2] Explanation: The sum of -1 and 0 is -1. Therefore index1 = 1,...
Read more

Comparable Vs. Comparator in Java

  In Java , Comparable and Comparator both are interfaces used to sort objects. Comparable It defines  natural ordering  within a class. It is implemented  inside  the class being sorted. It uses the compareTo() method. It allows sorting  by one one . Comparable provides a  single sorting sequence . In other words, we can sort the collection on the basis of a single element such as id, name, and price. Comparable  affects the original class , i.e., the actual class is modified. Comparable is present in  java.lang  package. We can sort the list elements of Comparable type by  Collections.sort(List)  method. Only one compareTo() method can be implemented, restricting flexibility. Comparator It defines  custom sorting logic It is implemented  in a separate class  or using lambda expressions . It uses the compare() method. It allows sorting  by multiple criteria . The Comparator provides  multiple sorting...
Read more

Increasing Triplet Subsequence

 Given an integer array nums, return true if there exists a triple of indices (i, j, k) such that i < j < k and nums[i] < nums[j] < nums[k]. If no such indices exists, return false.   Example 1: Input: nums = [1,2,3,4,5] Output: true Explanation: Any triplet where i < j < k is valid. Example 2: Input: nums = [5,4,3,2,1] Output: false Explanation: No triplet exists. Example 3: Input: nums = [2,1,5,0,4,6] Output: true Explanation: The triplet (3, 4, 5) is valid because nums[3] == 0 < nums[4] == 4 < nums[5] == 6. Brute Force : Failed for some testcase class Solution {     public boolean increasingTriplet ( int [] nums ) {         int n = nums . length ;         int i = 0 ;         int j =i+ 1 ;         int k =j+ 1 ;         while (i <n && j<n && k<n)         {         if (nums...
Read more