JavaScript Exercises: Print a singly linked list in reverse order

JavaScript Singly Linked List: Exercise-2 with Solution

Write a JavaScript program to create a singly linked list of n nodes and display it in reverse order.

Sample Solution:

JavaScript Code:

// Define a class representing a node in a singly linked list
class Node {
    constructor(data) {
        // Initialize the node with provided data
        this.data = data
        // Initialize the next pointer to null
        this.next = null                
    }
}

// Define a class representing a singly linked list
class SinglyLinkedList {
    constructor(Head = null) {
        // Initialize the head of the list
        this.Head = Head
    }

    // Method to add a new node to the end of the list
    add(newNode){
        // Start traversal from the head node
        let node = this.Head;
        // If the list is empty, set the new node as the head and return
        if(node == null){
            this.Head = newNode;
            return;
        }
        // Traverse the list until the last node
        while (node.next) {
            node = node.next;
        }
        // Set the next pointer of the last node to the new node
        node.next = newNode;
    }

    // Method to reverse the elements of the list
    reverse_list(){
        // Initialize variables to keep track of previous, current, and next nodes
        let prevNode = null;
        let currentNode = this.Head;
        // If the list is empty, return
        if(currentNode === null) return;

        let nextNode;
        // Traverse the list and reverse the next pointers of each node
        while(currentNode){
            nextNode = currentNode.next;
            currentNode.next = prevNode;
            prevNode = currentNode;
            currentNode = nextNode;
        }
        // Update the head of the list to the last node
        this.Head = prevNode;
    }
  
    // Method to display the elements of the list
    displayList(){
        // Start traversal from the head node
        let node = this.Head;
        // Initialize an empty string to store the elements of the list
        var str = ""
        // Traverse the list and concatenate each element to the string
        while (node) {
            str += node.data + "->";
            node = node.next;
        }
        // Append "NULL" to indicate the end of the list
        str += "NULL"
        // Print the string containing the list elements
        console.log(str);  
    } 
}

// Create an instance of the SinglyLinkedList class
let numList = new SinglyLinkedList();
// Add nodes with data values 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 elements of the list
console.log("Original Linked list:");
numList.displayList();
// Reverse the list
numList.reverse_list();
// Display the reversed elements of the list
console.log("Reverse Linked list:");
numList.displayList();

Output:

Original Linked list:
2->3->4->5->6->7->NULL
Reverse Linked list:
7->6->5->4->3->2->NULL

Flowchart:

Live Demo:

See the Pen javascript-singly-linked-list-exercise-2 by w3resource (@w3resource) on CodePen.

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