Node Structure and Pointer Design in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Node class with a constructor that initializes the value and next pointer.

DSA Javascript

class Node {
  constructor(value) {
    this.value = value;
    this.[1] = null;
  }
}

Drag options to blanks, or click blank then click option'

Alink

Bprev

Cpointer

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is for doubly linked lists

Using 'pointer' or 'link' which are not standard property names

The next property is used to point to the next node in a linked list.

2fill in blank

medium

Complete the code to link two nodes together by setting the next pointer of the first node.

DSA Javascript

const node1 = new Node(1);
const node2 = new Node(2);
node1.[1] = node2;

Drag options to blanks, or click blank then click option'

Aprev

Blink

Cnext

Dpointer

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is for previous nodes

Using 'link' or 'pointer' which are not standard properties

To link nodes in a singly linked list, set the next property of the first node to the second node.

3fill in blank

hard

Fix the error in the code to correctly create a doubly linked list node with previous and next pointers.

DSA Javascript

class Node {
  constructor(value) {
    this.value = value;
    this.next = null;
    this.[1] = null;
  }
}

Drag options to blanks, or click blank then click option'

Aprev

BpreviousNode

Cpointer

Dlast

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-standard property names

Forgetting to initialize the previous pointer

The standard property name for the pointer to the previous node in a doubly linked list is prev.

4fill in blank

hard

Fill both blanks to complete the function that creates a singly linked list node and sets its next pointer.

DSA Javascript

function createNode(value, nextNode) {
  return {
    value: value,
    [1]: nextNode
  };
}

const node = createNode(5, [2]);

Drag options to blanks, or click blank then click option'

Anext

Bprev

Cnull

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next'

Using 'undefined' instead of 'null' for no next node

The property to link to the next node is next. If there is no next node, it should be null.

5fill in blank

hard

Fill all three blanks to complete the Node class constructor for a doubly linked list.

DSA Javascript

class Node {
  constructor(value) {
    this.[1] = value;
    this.[2] = null;
    this.[3] = null;
  }
}

Drag options to blanks, or click blank then click option'

Avalue

Bprev

Cnext

Dpointer

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up 'prev' and 'next'

Using non-standard property names like 'pointer'

The constructor initializes value, prev for the previous node, and next for the next node.

Practice

1. What does a next pointer in a linked list node represent?

easy

A. It points to the previous node in the list

B. It points to the next node in the list

C. It stores the data of the node

D. It holds the size of the list

Solution

1. Step 1: Understand the role of next pointer

   The next pointer in a linked list node is used to link the current node to the following node, creating a chain.

2. Step 2: Differentiate from other parts of the node

   The data is stored separately in the node, and the next pointer does not hold data or list size. It specifically points to the next node.

3. Final Answer:

   It points to the next node in the list -> Option B

4. Quick Check:

   next pointer = next node address [OK]

Hint: Remember: next always points forward in the list [OK]

Common Mistakes:

• Confusing next with data storage
• Thinking next points backward
• Assuming next holds list size

2. Which of the following is the correct way to create a node object with a value and next pointer in JavaScript?

easy

A. const node = { value: 5, next: null };

B. const node = (value: 5, next: null);

C. const node = [value = 5, next = null];

D. const node = { val = 5, pointer = null };

Solution

1. Step 1: Identify correct JavaScript object syntax

   JavaScript objects use curly braces with key-value pairs separated by colons, like { key: value }.

2. Step 2: Check each option's syntax

   const node = { value: 5, next: null }; uses correct object syntax with keys value and next. Options B and C use invalid syntax, and D uses wrong keys.

3. Final Answer:

   const node = { value: 5, next: null }; -> Option A

4. Quick Check:

   Object with keys and colons = correct syntax [OK]

Hint: Use curly braces and colons for object properties [OK]

Common Mistakes:

• Using parentheses instead of braces
• Using equal signs instead of colons
• Wrong property names like val or pointer

3. What will be the output of the following code?

function Node(value) {
  this.value = value;
  this.next = null;
}

const first = new Node(1);
const second = new Node(2);
first.next = second;
console.log(first.next.value);

medium

A. undefined

B. 1

C. 2

D. null

Solution

1. Step 1: Understand node creation and linking

   Two nodes are created with values 1 and 2. The next of the first node points to the second node.

2. Step 2: Access the value of the node pointed by first.next

   first.next points to the second node, which has value 2, so first.next.value is 2.

3. Final Answer:

   2 -> Option C

4. Quick Check:

   first.next.value = 2 [OK]

Hint: Follow the next pointer to get the next node's value [OK]

Common Mistakes:

• Confusing first.value with first.next.value
• Expecting null instead of node value
• Not linking nodes before accessing next

4. Identify the error in the following code snippet for creating a linked list node:

function Node(value) {
  this.value = value;
  this.next = undefined;
}

const node = new Node(10);
console.log(node.next.value);

medium

A. The next pointer should be a number

B. Missing semicolon after new Node(10)

C. Node constructor should not use this

D. Accessing value of undefined causes error

Solution

1. Step 1: Analyze the next pointer initialization

   The next pointer is set to undefined, meaning it does not point to any node.

2. Step 2: Understand the error when accessing node.next.value

   Since node.next is undefined, trying to access value on it causes a runtime error.

3. Final Answer:

   Accessing value of undefined causes error -> Option D

4. Quick Check:

   Accessing property on undefined = error [OK]

Hint: Never access properties on null or undefined pointers [OK]

Common Mistakes:

• Assuming next can be undefined safely
• Thinking semicolon omission causes runtime error
• Believing this is invalid in constructor

5. You want to create a singly linked list with nodes containing values 1, 2, and 3 in order. Which code snippet correctly links the nodes?

hard

A. const n1 = { value: 1, next: null };
const n2 = { value: 2, next: null };
const n3 = { value: 3, next: null };
n1.next = n2;
n2.next = n3;

B. const n1 = { value: 1, next: null };
const n2 = { value: 2, next: null };
const n3 = { value: 3, next: null };
n3.next = n2;
n2.next = n1;

C. const n1 = { value: 1, next: null };
const n2 = { value: 2, next: null };
const n3 = { value: 3, next: null };
n1.next = n3;
n3.next = n2;

D. const n1 = { value: 1, next: null };
const n2 = { value: 2, next: null };
const n3 = { value: 3, next: null };
n2.next = n1;
n3.next = n2;

Solution

1. Step 1: Understand the order of nodes in a singly linked list

   The list should start at node with value 1, then point to node 2, then node 3, and finally null.

2. Step 2: Check the linking in each option

   const n1 = { value: 1, next: null }; const n2 = { value: 2, next: null }; const n3 = { value: 3, next: null }; n1.next = n2; n2.next = n3; links n1.next to n2 and n2.next to n3, which is correct. Other options link nodes in reverse or wrong order.

3. Final Answer:

   Option A links nodes in correct order 1 -> 2 -> 3 -> null -> Option A

4. Quick Check:

   Link nodes forward in order [OK]

Hint: Link each node's next to the next value in order [OK]

Common Mistakes:

• Linking nodes backward
• Skipping nodes in the chain
• Assigning next incorrectly