JavaScript Exercises: Get the value of a node at a given position in a Doubly Linked List

JavaScript Data Structures: Exercise-8 with Solution

Get the value of a node at a given position in a DLL

Write a JavaScript program to get the value of a node at a given position in 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 get the value of a node at a specified index
get_Node_Value(index) {
 if (index < 0 || index >= this.length) {
   return null; // Return null if the index is out of bounds
 }
 var current = this.head; // Start from the head of the list
 var count = 0;
 while (count < index) { // Iterate through the list until reaching the specified index
   current = current.next;
   count++;
 }
 return current.value; // Return the value of the node at the specified index
}
 // 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();
// Display the value of the node at index 1
console.log("Value at index 1:");
console.log(numList.get_Node_Value(1));
// Display the value of the node at index 5
console.log("Value at index 5:");
console.log(numList.get_Node_Value(5));
// Display the value of the node at index 11 (out of bounds)
console.log("Value at index 11:");
console.log(numList.get_Node_Value(11));

Output:

"Original Doubly Linked Lists:"
" 2 3 4 5 6 7"
"Value at index 1:"
2
"Value at index 5:"
6
"Value at index 11:"
null 

Flowchart:

Live Demo:

See the Pen javascript-doubly-linked-list-exercise-8 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that traverses a DLL to return the value of the node at a specified index.
• Write a JavaScript function that uses recursion to locate and return the data of a node at a given position in a DLL.
• Write a JavaScript function that validates the provided index and returns a default value if the index is out of range.
• Write a JavaScript function that iterates from the head of a DLL and returns the node’s value when a counter matches the desired index.

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