JavaScript Exercises: Remove the head element from a doubly Linked lists

JavaScript Data Structures: Exercise-15 with Solution

Remove the head element from a DLL

Write a JavaScript program that removes the head element from a doubly Linked lists.

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 both head and tail
   this.tail = newNode;
   }
   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
  }
remove_Head() {
   if (!this.head) { // If the list is empty, return null
     return null;
   }
   if (!this.head.next) { // If there is only one node in the list
     this.head = null; // Set head to null
     this.tail = null; // Also set tail to null
     return;
   }
   this.head = this.head.next; // Update the head to the next node
   this.head.previous = null; // Set the previous pointer of the new head to null
   this.length--; // Decrement the length of the list
 }
 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 Head element:"); // Remove the head element
numList.remove_Head();
numList.printList();
console.log("Remove the Head element:"); // Remove the head element again
numList.remove_Head();
numList.printList();

Output:

Original Doubly Linked Lists:
 2 3 4 5 6 7
Remove the Head element:
2 3 4 5 6 7
Remove the Head element:
3 4 5 6 7

Flowchart:

Live Demo:

See the Pen javascript-doubly-linked-list-exercise-15 by w3resource (@w3resource) on CodePen.

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