Linked List vs Array When to Choose Which in DSA Typescript - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array in TypeScript.

DSA Typescript

const numbers: number[] = [1];

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

A<1, 2, 3>

B(1, 2, 3)

C{1, 2, 3}

D[1, 2, 3]

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses () instead of square brackets.

Using curly braces {} which are for objects.

The correct syntax to declare an array literal in TypeScript uses square brackets [].

2fill in blank

medium

Complete the code to create a simple linked list node class in TypeScript.

DSA Typescript

class ListNode {
  value: number;
  next: ListNode | null;
  constructor(value: number) {
    this.value = value;
    this.next = [1];
  }
}

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

Anull

Bundefined

C0

Dthis

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined instead of null.

Assigning 0 or this which are incorrect.

In a linked list, the next pointer is null when there is no next node.

3fill in blank

hard

Fix the error in the function that adds an element to the end of a linked list.

DSA Typescript

function appendNode(head: ListNode | null, value: number): ListNode {
  const newNode = new ListNode(value);
  if (head === null) {
    return newNode;
  }
  let current = head;
  while (current.next !== [1]) {
    current = current.next;
  }
  current.next = newNode;
  return head;
}

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

A0

Bundefined

Cnull

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined or 0 which are not correct end markers.

Using head which is the start, not the end.

The loop should continue until current.next is null, meaning the end of the list.

4fill in blank

hard

Fill both blanks to create a function that converts an array to a linked list.

DSA Typescript

function arrayToLinkedList(arr: number[]): ListNode | null {
  if (arr.length === 0) return null;
  const head = new ListNode(arr[0]);
  let current = head;
  for (let i = 1; i [1] arr.length; i++) {
    current.next = new ListNode(arr[[2]]);
    current = current.next;
  }
  return head;
}

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

A<

B<=

Ci

Di - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causes out of bounds error.

Using i - 1 accesses wrong array element.

The loop runs while i is less than arr.length, and the current node's next is set to a new node with arr[i].

5fill in blank

hard

Fill all three blanks to create a function that converts a linked list back to an array.

DSA Typescript

function linkedListToArray(head: ListNode | null): number[] {
  const result: number[] = [];
  let current = [1];
  while (current !== [2]) {
    result.push(current.[3]);
    current = current.next;
  }
  return result;
}

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

Ahead

Bnull

Cvalue

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using next instead of value when pushing to array.

Looping until current is undefined instead of null.

Start from head, loop until current is null, and push current.value to the array.

Practice

1. Which data structure is better when you need fast random access to elements by index?

easy

A. Stack

B. Linked List

C. Array

D. Queue

Solution

1. Step 1: Understand random access in arrays

   Arrays store elements in contiguous memory, so accessing by index is fast and direct.

2. Step 2: Understand random access in linked lists

   Linked lists require traversal from the head to reach an index, which is slower.

3. Final Answer:

   Array -> Option C

4. Quick Check:

   Fast random access = Array [OK]

Hint: Arrays give fast index access; linked lists do not [OK]

Common Mistakes:

• Thinking linked lists allow fast index access
• Confusing stack or queue with arrays
• Assuming all data structures have same access speed

2. Which of the following is the correct way to declare an empty linked list node in TypeScript?

easy

A. const node = new LinkedListNode(null);

B. const node = new LinkedListNode();

C. const node = LinkedListNode();

D. const node = LinkedListNode(null);

Solution

1. Step 1: Understand TypeScript class instantiation

   To create an instance, use the 'new' keyword with constructor parameters.

2. Step 2: Check constructor parameters

   LinkedListNode usually requires a value; null can represent empty data.

3. Final Answer:

   const node = new LinkedListNode(null); -> Option A

4. Quick Check:

   Use 'new' with constructor args for instances [OK]

Hint: Use 'new' keyword with constructor parameters to create nodes [OK]

Common Mistakes:

• Omitting 'new' keyword
• Calling class like a function without 'new'
• Passing no arguments when constructor expects one

3. Given this TypeScript code, what is the printed output?

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

const head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);

let current = head;
const result: number[] = [];
while (current !== null) {
  result.push(current.value);
  current = current.next;
}
console.log(result);

medium

A. [1, 2, 3]

B. [3, 2, 1]

C. [1, 3, 2]

D. []

Solution

1. Step 1: Build the linked list nodes

   Nodes created with values 1, 2, 3 linked in order: 1 -> 2 -> 3 -> null.

2. Step 2: Traverse and collect values

   Loop pushes values 1, then 2, then 3 into result array.

3. Final Answer:

   [1, 2, 3] -> Option A

4. Quick Check:

   Traverse linked list in order = [1, 2, 3] [OK]

Hint: Traverse linked list from head to null to get values in order [OK]

Common Mistakes:

• Confusing order of nodes
• Not updating current pointer correctly
• Expecting reversed output

4. This TypeScript code tries to insert a new node at the start of a linked list but has a bug. What is the error?

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

let head = new Node(1);
head.next = new Node(2);

function insertAtStart(newValue: number) {
  const newNode = new Node(newValue);
  newNode.next = head.next;
  head = newNode;
}

insertAtStart(0);

let current = head;
const result: number[] = [];
while (current !== null) {
  result.push(current.value);
  current = current.next;
}
console.log(result);

medium

A. head should not be reassigned inside the function

B. newNode.next should point to head, not head.next

C. Node constructor missing initialization of next

D. insertAtStart should return the new head

Solution

1. Step 1: Analyze insertion logic

   New node's next is set to head.next, skipping the current head node.

2. Step 2: Correct pointer assignment

   To insert at start, newNode.next must point to current head, preserving the list.

3. Final Answer:

   newNode.next should point to head, not head.next -> Option B

4. Quick Check:

   Insert at start = newNode.next = head [OK]

Hint: New head's next must link to old head, not old head's next [OK]

Common Mistakes:

• Setting newNode.next to head.next causes node loss
• Not updating head reference properly
• Confusing next pointers in linked list

5. You need to frequently insert and delete elements in the middle of a large collection. Which data structure is better and why? A) Array, because it allows fast random access. B) Linked List, because it supports binary search efficiently. C) Array, because it uses less memory. D) Linked List, because it allows fast insertion and deletion without shifting elements.

hard

A. Array, because it allows fast random access.

B. Linked List, because it supports binary search efficiently.

C. Array, because it uses less memory.

D. Linked List, because it allows fast insertion and deletion without shifting elements.

Solution

1. Step 1: Consider insertion and deletion in arrays

   Arrays require shifting elements when inserting or deleting in the middle, which is slow.

2. Step 2: Consider linked list advantages

   Linked lists can insert or delete nodes by changing pointers without shifting elements, making these operations faster.

3. Final Answer:

   Linked List, because it allows fast insertion and deletion without shifting elements. -> Option D

4. Quick Check:

   Frequent middle insert/delete = Linked List [OK]

Hint: Linked lists excel at middle insert/delete without shifting [OK]

Common Mistakes:

• Choosing array for frequent middle insert/delete
• Thinking linked lists support binary search efficiently
• Ignoring cost of shifting elements in arrays