Node Structure and Pointer Design in DSA Javascript - Build from Scratch

Node Structure and Pointer Design

📖 Scenario: Imagine you are building a simple train where each carriage is connected to the next one. Each carriage holds a number, and you want to create this train in code using nodes and pointers.

🎯 Goal: You will create a node structure in JavaScript where each node holds a number and a pointer to the next node. Then, you will link two nodes together and finally print the linked nodes to see the connection.

📋 What You'll Learn

Create a Node class with value and next properties

Create two nodes with values 10 and 20

Link the first node's next pointer to the second node

Print the values of the nodes showing the connection

💡 Why This Matters

🌍 Real World

Node structures and pointers are the foundation of linked lists, which are used in many applications like music playlists, undo functionality in apps, and navigation systems.

💼 Career

Understanding node structures and pointers is essential for software developers working with data structures, memory management, and building efficient algorithms.

1

Create the Node class

Create a class called Node with a constructor that takes a parameter value. Inside the constructor, set this.value to value and this.next to null.

DSA Javascript

class Node {
  constructor(value) {
    // Your code here
  }
}

Hint

Think of this.value as the number in the carriage and this.next as the pointer to the next carriage.

2

Create two nodes

Create two variables called node1 and node2. Set node1 to a new Node with value 10 and node2 to a new Node with value 20.

DSA Javascript

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

// Your code here

Hint

Use the new keyword to create instances of the Node class.

3

Link the nodes

Set the next property of node1 to point to node2.

DSA Javascript

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

const node1 = new Node(10);
const node2 = new Node(20);

// Your code here

Hint

Think of node1.next as the pointer from the first carriage to the second carriage.

4

Print the linked nodes

Print the value of node1 and the value of the node that node1.next points to, separated by ' -> '. Use console.log.

DSA Javascript

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

const node1 = new Node(10);
const node2 = new Node(20);

node1.next = node2;

// Your code here

Hint

Print the chain like a train: first carriage value, arrow, second carriage value, arrow, and then 'null' to show the end.

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