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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an empty array in JavaScript.

DSA Javascript

const myArray = [1];

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

Anull

B{}

C[]

Dnew Array()

Attempts:

3 left

💡 Hint

Common Mistakes

Using curly braces {} creates an object, not an array.

Using null does not create an array.

Using new Array() works but is less common for empty arrays.

In JavaScript, an empty array is created using square brackets [].

2fill in blank

medium

Complete the code to add a new node at the start of a linked list.

DSA Javascript

function addAtStart(head, value) {
  const newNode = { data: value, next: [1] };
  return newNode;
}

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

Ahead

Bnull

Cundefined

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to null breaks the list.

Using undefined causes errors.

Using value instead of a node reference is incorrect.

To add a node at the start, the new node's next should point to the current head.

3fill in blank

hard

Fix the error in the code that removes the last element from an array.

DSA Javascript

function removeLast(arr) {
  arr.[1]();
  return arr;
}

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

Apush

Bpop

Cshift

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using shift() removes the first element, not the last.

Using push() adds elements instead of removing.

Using unshift() adds elements at the start.

The pop() method removes the last element from an array.

4fill in blank

hard

Fill both blanks to create a linked list node and link it to the next node.

DSA Javascript

const nextNode = { data: 10, [1]: null };
const node = { data: 5, [2]: nextNode };

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

Anext

Bprev

Cvalue

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' breaks forward linking.

Using 'value' or 'head' as pointer names is incorrect.

Linked list nodes use the 'next' property to point to the next node.

5fill in blank

hard

Fill all three blanks to create an array of node data values from a linked list.

DSA Javascript

function listToArray(head) {
  const result = [];
  let current = head;
  while (current [1] null) {
    result.[2](current.[3]);
    current = current.next;
  }
  return result;
}

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

A!==

Bpush

Cdata

D===

Attempts:

3 left

💡 Hint

Common Mistakes

Using === instead of !== causes the loop to skip.

Using pop() instead of push() removes elements.

Accessing current.value instead of current.data is incorrect.

The loop continues while current is not null, pushing current.data into the array.

Practice

1. Which data structure is generally better for frequent insertions and deletions in the middle of the collection?

easy

A. Array

B. Neither is suitable

C. Both are equally efficient

D. Linked List

Solution

1. Step 1: Understand insertion and deletion costs in arrays

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

2. Step 2: Understand linked list insertion and deletion

   Linked lists can insert or delete nodes by changing pointers without shifting elements.

3. Final Answer:

   Linked List -> Option D

4. Quick Check:

   Insert/delete middle = Linked List [OK]

Hint: Choose linked list for fast middle insert/delete [OK]

Common Mistakes:

• Thinking arrays handle middle insertions efficiently
• Confusing array resizing with insertion cost
• Assuming linked lists have faster access

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

easy

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

B. const node = [null, null];

C. const node = null;

D. const node = new Array();

Solution

1. Step 1: Understand linked list node structure

   A linked list node typically has a value and a pointer to the next node, represented as an object with 'value' and 'next' properties.

2. Step 2: Check each option

   const node = { value: null, next: null }; correctly creates an object with 'value' and 'next' set to null. Others do not represent a linked list node properly.

3. Final Answer:

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

4. Quick Check:

   Linked list node = object with value and next [OK]

Hint: Linked list nodes are objects with value and next [OK]

Common Mistakes:

• Using arrays instead of objects for nodes
• Assigning null directly without properties
• Confusing array declaration with node

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

const arr = [1, 2, 3];
arr.splice(1, 1, 4);
console.log(arr);

medium

A. [1, 4, 3]

B. [1, 2, 3]

C. [4, 2, 3]

D. [1, 3]

Solution

1. Step 1: Understand splice parameters

   arr.splice(1, 1, 4) means start at index 1, remove 1 element, then insert 4 at that position.

2. Step 2: Apply splice to array

   Original array is [1, 2, 3]. Removing element at index 1 (which is 2) and inserting 4 results in [1, 4, 3].

3. Final Answer:

   [1, 4, 3] -> Option A

4. Quick Check:

   splice replaces element at index 1 with 4 [OK]

Hint: splice(start, deleteCount, item) replaces elements [OK]

Common Mistakes:

• Thinking splice inserts without deleting
• Confusing splice with slice
• Expecting original array unchanged

4. Identify the error in the following linked list insertion code snippet:

function insertAtHead(head, value) {
  const newNode = { value: value, next: head };
  head = newNode;
  return head;
}

let head = null;
insertAtHead(head, 5);
console.log(head);

medium

A. newNode is not created correctly

B. The head variable is not updated outside the function

C. The function should not return head

D. The next pointer should be null

Solution

1. Step 1: Understand variable scope in JavaScript

   Inside the function, head is a local parameter. Assigning head = newNode changes only local copy.

2. Step 2: Check effect on external head variable

   Outside the function, head remains null because the updated head inside the function is not reflected outside.

3. Final Answer:

   The head variable is not updated outside the function -> Option B

4. Quick Check:

   Function parameter reassignment doesn't affect external variable [OK]

Hint: Return and assign new head to update linked list [OK]

Common Mistakes:

• Assuming head changes globally without return
• Not returning the new head
• Misunderstanding pointer assignment

5. You need to store a large collection of items where you frequently add elements at the end and access elements by index quickly. Which data structure should you choose and why?

hard

A. Linked List, because it allows fast access by index

B. Linked List, because it uses less memory than arrays

C. Array, because it allows fast access by index and efficient append

D. Array, because it allows fast insertion and deletion in the middle

Solution

1. Step 1: Analyze access by index requirement

   Arrays provide constant time access by index, linked lists require traversal which is slower.

2. Step 2: Analyze frequent append requirement

   Arrays can append efficiently if capacity allows; linked lists also append efficiently but slower access is a drawback.

3. Final Answer:

   Array, because it allows fast access by index and efficient append -> Option C

4. Quick Check:

   Fast index access + append = Array [OK]

Hint: Use array for fast index access and appending [OK]

Common Mistakes:

• Choosing linked list for fast index access
• Assuming linked list uses less memory always
• Confusing insertion in middle with append