JavaScript Exercises: Print a Doubly Linked lists in reverse order

JavaScript Data Structures: Exercise-9 with Solution

Create a DLL of n nodes and display in reverse

Write a JavaScript program to create a Doubly Linked lists of n nodes and display it in reverse order.

Sample Solution:

JavaScript Code:

// Define a class for creating nodes of a doubly linked list
class Node {
	constructor(value) {
		this.value = value; // Store the value of the node
		this.next = null; // Pointer to the next node in the list, initially set to null
		this.previous = null; // Pointer to the previous node in the list, initially set to null
	}
}

// Define a class for creating a doubly linked list
class DoublyLinkedList {
	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
	}

	// Method to add a new node at the end of the list
	add(newNode) {
		// Check if the head is null, indicating an empty list
		if (this.head === null) {
			this.head = newNode; // Set the head to the new node
			this.tail = newNode; // Set the tail to the new node
		} else {
			newNode.previous = this.tail; // Set the previous pointer of the new node to the current tail
			this.tail.next = newNode; // Set the next pointer of the current tail to the new node
			this.tail = newNode; // Update the tail to the new node
		}
		this.length++; // Increment the length of the list
	}

	// Method to reverse the doubly linked list
	reverse() {
		let current = this.head; // Start from the head of the list
		let temp = null; // Temporary variable to store the previous node during reversal
		while (current != null) {
			temp = current.previous; // Store the previous node
			current.previous = current.next; // Swap the previous and next pointers of the current node
			current.next = temp;
			current = current.previous; // Move to the next node
		}
		if (temp != null) {
			this.head = temp.previous; // Update the head pointer to the last node after reversal
		}
		return this.head; // Return the head of the reversed list
	}

	// Method to print the values of the nodes in 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) {
			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
	}
}

// Create a new instance of the DoublyLinkedList class
let numList = new DoublyLinkedList();

// Add nodes to the list
numList.add(new Node(2));
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));

// Display the original doubly linked list
console.log("Original Doubly Linked List:");
numList.printList();

// Reverse the linked list and display it
console.log("Reverse Linked List:");
numList.reverse();
numList.printList();

Output:

Original Doubly Linked Lists:
 2 3 4 5 6 7
Reverse Linked list:
7 6 5 4 3 2 

Flowchart:

Live Demo:

See the Pen javascript-doubly-linked-list-exercise-9 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that constructs a doubly linked list with n nodes and then prints the list in reverse order using the tail pointer.
• Write a JavaScript function that traverses a DLL backwards from the tail to the head and displays each node’s data.
• Write a JavaScript function that verifies reverse traversal by comparing the output with an array of node values reversed.
• Write a JavaScript function that creates a DLL from an array and displays its elements in reverse order using a while loop.

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