JavaScript Exercises: Remove a node at the specified index in a Doubly linked lists

JavaScript Data Structures: Exercise-14 with Solution

Remove the node from a DLL at the specified index

Write a JavaScript program that removes the node from the Doubly linked lists at the specified index.

Sample Solution:

JavaScript Code:

class Node {
         // Constructor function for creating a new node with a given value
         constructor(value) {
                  this.value = value; // Assign the given value to the node
                  this.next = null; // Initialize the pointer to the next node as null
                  this.previous = null; // Initialize the pointer to the previous node as null
         }
}
class DoublyLinkedList {
         // Constructor function for creating a new doubly linked list with a head node having the given value
         constructor(value) {
                  // Initialize the head node with the given value and no next or previous node
                  this.head = {
                            value: value, // Store the value of the head node
                            next: null, // Pointer to the next node in the list, initially set to null
                            previous: null // Pointer to the previous node in the list, initially set to null
                  };
                  this.length = 0; // Initialize the length of the list to 0
                  this.tail = this.head; // Set the tail node to the head node initially
         }
 add(newNode) {
   if (this.head === null) {
   this.head = newNode; // If the list is empty, set the new node as the head
   this.tail = newNode; // Also set the new node as the tail
   }
   else
   {
   newNode.previous = this.tail; // Set the previous pointer of the new node to the current tail node
   this.tail.next = newNode; // Set the next pointer of the current tail node to the new node
   this.tail = newNode; // Update the tail node to the new node
   }
    this.length++; // Increment the length of the list
  }
 delete(index) {
   if (index < 0 || index >= this.length) return null; // Check if the index is valid
   if (index === 0) return this.shift(); // If index is 0, remove the first node
   if (index === this.length - 1) return this.pop(); // If index is the last one, remove the last node
   let current = this.head; // Start from the head of the list
   let ctr = 0; // Counter to track the index
   while (ctr !== index) { // Iterate until reaching the node to be removed
     current = current.next; // Move to the next node
     ctr++; // Increment the counter
   }
   current.previous.next = current.next; // Adjust the next pointer of the previous node
   current.next.previous = current.previous; // Adjust the previous pointer of the next node
   this.length--; // Decrement the length of the list
   return current; // Return the removed node
 }
 shift() {
   if (!this.head) return null; // Check if the list is empty
   let old_Head = this.head; // Store the reference to the current head node
   if (this.length === 1) { // Check if there is only one node in the list
     this.head = null; // If yes, set head to null
     this.tail = null; // Also set tail to null
   } else { // If there are more than one node in the list
     this.head = old_Head.next; // Update the head to the next node
     this.head.previous = null; // Set the previous pointer of the new head to null
     old_Head.next = null; // Set the next pointer of the old head to null
   }
   this.length--; // Decrement the length of the list
   return old_Head; // Return the removed node (old head)
 }
 pop() {
   if (!this.tail) return null; // Check if the list is empty
   let pNode = this.tail; // Store the reference to the current tail node
   if (this.length === 1) { // Check if there is only one node in the list
     this.head = null; // If yes, set head to null
     this.tail = null; // Also set tail to null
   } else { // If there are more than one node in the list
     this.tail = pNode.previous; // Update the tail to the previous node
     this.tail.next = null; // Set the next pointer of the new tail to null
     pNode.previous = null; // Set the previous pointer of the old tail to null
   }
   this.length--; // Decrement the length of the list
   return pNode; // Return the removed node (old tail)
 }
 printList(){

                  let current = this.head; // Start from the head of the list
                  let result = []; // Array to store the values of the nodes
                  while (current !== null) { // Iterate through the list until reaching the end
                            result.push(current.value); // Push the value of the current node to the array
                            current = current.next; // Move to the next node
                  }
                  console.log(result.join(' ')); // Log the values of the nodes separated by space
                  return this; // Return the DoublyLinkedList object for chaining
          }
}
let numList = new DoublyLinkedList(); // Create a new instance of the DoublyLinkedList class
numList.add(new Node(2)); // Add nodes to the list
numList.add(new Node(3));
numList.add(new Node(4));
numList.add(new Node(5));
numList.add(new Node(6));
numList.add(new Node(7));
console.log("Original Doubly Linked Lists:"); // Print the original list
numList.printList();
console.log("Remove the node,index = 5");
numList.delete(5)
numList.printList();
console.log("Remove the node,index = 4");
numList.delete(4)
numList.printList();
console.log("Remove the node,index = 2");
numList.delete(2)
numList.printList();

Output:

Original Doubly Linked Lists:
 2 3 4 5 6 7
Remove the node,index = 5
 2 3 4 5 6
Remove the node,index = 4
 2 3 4 5
Remove the node,index = 2
 2 4 5

Flowchart:

Live Demo:

See the Pen javascript-doubly-linked-list-exercise-14 by w3resource (@w3resource) on CodePen.

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