Node Structure and Pointer Design in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a node in data structures like linked lists?

A node is a basic unit that holds data and a reference (pointer) to the next node, allowing the creation of chains or lists.

beginner

What does a pointer in a node represent?

A pointer is a reference or link from one node to another, showing where the next node is located in the structure.

beginner

In a singly linked list node, how many pointers are there and what do they point to?

There is one pointer that points to the next node in the list or null if it is the last node.

beginner

Why is the pointer in the last node of a linked list usually set to null?

Because it marks the end of the list, showing there is no next node to go to.

intermediate

How does a doubly linked list node differ in pointer design from a singly linked list node?

A doubly linked list node has two pointers: one to the next node and one to the previous node, allowing movement in both directions.

What does a node in a linked list typically contain?

A Data and a pointer to the next node

B Only data

C Only a pointer

D Data and a pointer to the previous node only

A node usually contains data and a pointer to the next node to form the linked list.

In a singly linked list, what does the pointer in the last node point to?

A Null

B The first node

C Itself

D The previous node

The last node's pointer is set to null to indicate the end of the list.

How many pointers does a node in a doubly linked list have?

A One

B Two

C Three

D None

A doubly linked list node has two pointers: one to the next node and one to the previous node.

What is the main purpose of pointers in node structures?

A To store data

B To sort nodes

C To delete nodes

D To link nodes together

Pointers link nodes together to form the data structure.

Which of the following best describes a pointer in a node?

A A function to process data

B A value that holds data

C A reference to another node

D A type of data

A pointer is a reference to another node in the structure.

Explain the structure of a node in a singly linked list and how pointers are used.

Think about how nodes connect to form a chain.

Describe the difference between pointer design in singly linked lists and doubly linked lists.

Consider how you can move forward and backward in the list.

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