Linked-List.js

// Define a Node class to represent a node in a singly linked list

class Node {
  constructor(data) {
    this.data = data; // Initialize node data
    this.next = null; // Initialize reference to the next node as null
  }
}

// Define a SLinkedList class to represent a singly linked list

class SLinkedList {

  constructor() {
    this.head = null; // Initialize the head of the list as null
    this.tail = null; // Initialize the tail of the list as null
  }
  
  // Method to add a new node to the end of the list

  addNode(data) {

    const newNode = new Node(data); // Create a new node with given data
    
    // If the list is empty, set the head as the new node
    if (this.head == null) {
      this.head = newNode;
    } else {
      this.tail.next = newNode; // Set the next reference of the tail to the new node
    }
    
    this.tail = newNode; // Set the new node as the tail of the list
  }
  
  // Method to display the list

  display() {
    // If the list is empty, print a message and return
    if (this.head == null) {
      const result = "List is Empty.";
      console.log(result);
      return result;
    }
    
    let temp = this.head; // Start from the head node
    
    while (temp != null) { // Iterate through the list
      console.log(temp.data + "=>"); // Print the data of each node
      temp = temp.next; // Move to the next node
    }

    if (temp == null) { // If we have reached the end of the list, print a message
      const result = "Completed printing the list.";
      console.log(result);
      return result;
    }
  }
  
  // Method to delete a node with given data from the list

  deleteNode(data) {

    // If the list is empty
    if (this.head == null) {
      this.tail = null; // Update the tail as there are no nodes left
      const result = "List is Empty.";
      console.log(result);
      return result;
    }

    let temp = this.head; // Start from the head node
    let prev = null; // Initialize a variable to keep track of the previous node
    
    // If the head node itself contains the data to be deleted, update the head and return
    if (temp != null && temp.data == data) {
      this.head = temp.next;
      const result = "Deleted head of the list.";
      console.log(result);
      return result;
    }
    
    // Iterate through the list to find the node with given data
    while (temp != null && temp.data != data) {
      prev = temp;
      temp = temp.next;
    }
    
    if (temp == null) { // If the data was not found, return
      const result = "Target Data not found in the list."
      console.log(result);
      return result;
    }
    
    // If the tail node contains the data to be deleted, update the tail and return
    if (temp == this.tail) {
      this.tail = prev;
      this.tail.next = null;
      return;
    }
    
    /*
      If a Node in the list which is not head or not tail and has the target data to delete.
      Remove the node with target data by updating the next reference of the previous node.
    */
    prev.next = temp.next; // This will delete the node after prev (ie, the node before temp) that has the target data to delete from the list.

  }

  // Method to reverse a linked list

  reverseLinkedList() {
      
    let currentNode = this.head;

    this.head = this.tail;

    this.tail = currentNode;

    let nextNode = null;

    let prevNode = null;

    while (currentNode !== null){

      nextNode = currentNode.next;

      currentNode.next = prevNode;

      prevNode = currentNode;

      currentNode = nextNode;
    }

  }

  countNodes(){

    let count = 0;

    if(this.head == null){
      const result = "Empty List";
      console.log(result);
      return result;
    }

    let currentNode = this.head;

    while(currentNode !== null){

      currentNode = currentNode.next;

      count++;

    }

    const result = `The total number of nodes in the given list is: ${count}`;
    console.log(result);
    return result;

  }

}

// =============Creating LINKED LISTS and processing various operations in a LINKED LIST=============

// Creating two linked lists

const list1 = new SLinkedList();
const list2 = new SLinkedList();

// Add nodes to the first linked list
list1.addNode(10);
list1.addNode(20);
list1.addNode(30);
list1.addNode(40);

// Display the first linked list
// list1.display();

// Add nodes to the second linked list
list2.addNode(100);
list2.addNode(200);
list2.addNode(300);
list2.addNode(400);

// Display the Second list
// list2.display();

// Delete a node from the first linked list

// list2.deleteNode(300);  // Deleting the node with the value 300

// Display the Second linked list

list2.display();

// Reversing a linked list

list2.reverseLinkedList();

// Displaying the reversed linked list

list2.display();