Linked List vs Array When to Choose Which in DSA Typescript - Key Differences

Recall & Review

beginner

What is a key advantage of using an array over a linked list?

Arrays provide fast access to elements by index because they store elements in contiguous memory locations.

beginner

Why might you choose a linked list instead of an array?

Linked lists allow easy insertion and deletion of elements without shifting other elements, making them better for dynamic data where size changes often.

beginner

What is a disadvantage of arrays compared to linked lists?

Arrays have a fixed size, so resizing requires creating a new array and copying elements, which can be costly.

intermediate

How does memory usage differ between arrays and linked lists?

Arrays use less memory per element because they store only data, while linked lists store data plus pointers to next elements, increasing memory overhead.

beginner

When is an array a better choice than a linked list?

When you need fast random access to elements and the number of elements is known or changes rarely.

Which data structure allows fast insertion and deletion at any position without shifting elements?

A Queue

B Array

C Linked List

D Stack

Linked lists store elements with pointers, so insertion and deletion do not require shifting other elements.

What is a downside of using linked lists compared to arrays?

A Contiguous memory allocation

B Fixed size

C No pointers

D Slower random access

Linked lists require traversal from the head to access elements, making random access slower than arrays.

When should you prefer arrays over linked lists?

A When you frequently insert in the middle

B When you need fast random access

C When memory overhead is not a concern

D When data size changes often

Arrays provide constant-time access by index, making them better for fast random access.

Which data structure uses extra memory for storing pointers?

A Linked List

B Array

C Hash Table

D Binary Tree

Linked lists store pointers to the next element, increasing memory usage compared to arrays.

What happens when you insert an element in the middle of an array?

A Elements after the position are shifted

B Pointer is updated

C No change needed

D Array size decreases

Inserting in an array requires shifting elements after the insertion point to make space.

Explain when you would choose a linked list over an array and why.

Think about how data changes and access speed.

Describe the main differences in memory usage and access speed between arrays and linked lists.

Consider how elements are stored and accessed.

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