JavaScript Exercises: Insert a new node at the beginning of a Doubly Linked List

JavaScript Data Structures: Exercise-6 with Solution

Write a JavaScript program to insert a new node at the beginning of a Doubly Linked List.

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 insert a new node at a specified position in the list
	insertAt(position, data) {
		if (position < 0 || position > this.length) {
			return false; // Return false if the position is invalid
		}
		var newNode = { // Create a new node with the given data
			value: data,
			next: null,
			previous: null
		};
		if (this.length === 0) { // If the list is empty, set the head and tail to the new node
			this.head = newNode;
			this.tail = newNode;
		} else if (position === 0) { // If inserting at the beginning, update the head
			newNode.next = this.head;
			this.head.previous = newNode;
			this.head = newNode;
		} else if (position === this.length) { // If inserting at the end, update the tail
			this.tail.next = newNode;
			newNode.previous = this.tail;
			this.tail = newNode;
		} else { // Otherwise, find the position and insert the new node
			var current = this.head;
			var index = 0;
			while (index < position) {
				current = current.next;
				index++;
			}
			newNode.next = current;
			newNode.previous = current.previous;
			current.previous.next = newNode;
			current.previous = newNode;
		}
		this.length++; // Increment the length of the list
		return true; // Return true to indicate successful insertion
	}

	// Method to insert a new node at the first position in the list
	insertFirst(value) {
		this.insertAt(0, value); // Call the insertAt method with the first position
	}

	// 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) { // 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
	}
}

// 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();
// Insert a new node at the first position with value 12
console.log("Insert at first position and value = 12");
numList.insertFirst(12);
numList.printList();
// Insert another new node at the first position with value 14
console.log("Again insert at first position and value = 14");
numList.insertFirst(14);
numList.printList();

Output:

Original Doubly Linked Lists:
 2 3 4 5 6 7
Insert at frist position and value = 12
12  2 3 4 5 6 7
Again insert at frist position and value = 14
14 12  2 3 4 5 6 7

Flowchart:

Live Demo:

See the Pen javascript-doubly-linked-list-exercise-6 by w3resource (@w3resource) on CodePen.

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