Memory Layout Comparison Array vs Linked List in DSA Javascript - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array with 3 elements.

DSA Javascript

const arr = [1, 2, [1]];

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

A3

B4

C5

D6

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number outside the sequence like 4 or 5.

The array is declared with elements 1, 2, and 3.

2fill in blank

medium

Complete the code to create a linked list node with value 10.

DSA Javascript

function Node(value) {
  this.value = value;
  this.next = [1];
}
const node = new Node(10);

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

Anull

Bundefined

C0

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined or 0 instead of null for the next pointer.

The next pointer of a new node is set to null to indicate the end of the list.

3fill in blank

hard

Fix the error in the code to link two nodes correctly.

DSA Javascript

const first = new Node(1);
const second = new Node(2);
first.next = [1];

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

Aundefined

Bsecond

Cnull

Dfirst

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning first to first.next causes a cycle.

Using null breaks the link.

The first node's next pointer should point to the second node to link them.

4fill in blank

hard

Fill both blanks to create an array and a linked list node with value 5.

DSA Javascript

const arr = [[1]];
const node = new Node([2]);

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

A5

B10

C15

D20

Attempts:

3 left

💡 Hint

Common Mistakes

Using different values for array and node.

Both the array and the node hold the value 5.

5fill in blank

hard

Fill all three blanks to complete the linked list traversal and print values.

DSA Javascript

let current = [1];
while (current !== [2]) {
  console.log(current.[3]);
  current = current.next;
}

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 to print.

Looping until current is undefined.

Start from head, loop until current is null, print current.value each step.

Practice

1. Which of the following best describes how elements are stored in an array compared to a linked list?

easy

A. Both array and linked list elements are stored contiguously in memory.

B. Array elements are scattered in memory, while linked list nodes are stored contiguously.

C. Array elements are stored in contiguous memory locations, while linked list nodes are scattered in memory.

D. Both array and linked list elements are scattered randomly in memory.

Solution

1. Step 1: Understand array memory layout

   Arrays store elements in contiguous memory blocks, meaning elements are next to each other in memory.

2. Step 2: Understand linked list memory layout

   Linked list nodes are allocated separately and linked by pointers, so they can be scattered in memory.

3. Final Answer:

   Array elements are stored in contiguous memory locations, while linked list nodes are scattered in memory. -> Option C

4. Quick Check:

   Array = contiguous, Linked List = scattered [OK]

Hint: Remember: arrays are like books on a shelf, linked lists like scattered notes [OK]

Common Mistakes:

• Thinking linked list nodes are stored contiguously
• Confusing array scattered storage with linked list
• Assuming both have same memory layout

2. Which syntax correctly declares an array and a linked list node in JavaScript?

easy

A. const arr = [1, 2, 3]; const node = { value: 1, next: null };

B. const arr = {1, 2, 3}; const node = [value: 1, next: null];

C. const arr = (1, 2, 3); const node = {1, null};

D. const arr = new LinkedList(); const node = [1, null];

Solution

1. Step 1: Check array declaration syntax

   Arrays in JavaScript are declared with square brackets, e.g., [1, 2, 3].

2. Step 2: Check linked list node syntax

   A linked list node is an object with properties like value and next, e.g., { value: 1, next: null }.

3. Final Answer:

   const arr = [1, 2, 3]; const node = { value: 1, next: null }; -> Option A

4. Quick Check:

   Array uses [], node uses object {} [OK]

Hint: Arrays use [], linked list nodes use objects {} [OK]

Common Mistakes:

• Using curly braces for arrays
• Using array syntax for linked list nodes
• Mixing parentheses for array declaration

3. Consider the following code snippet:

const arr = [10, 20, 30];
const node1 = { value: 10, next: null };
const node2 = { value: 20, next: node1 };
const node3 = { value: 30, next: node2 };

console.log(arr[1]);
console.log(node3.next.value);

What will be the output?

medium

A. 20 and 10

B. 20 and 20

C. 10 and 20

D. 30 and 20

Solution

1. Step 1: Evaluate array access

   arr[1] accesses the second element of the array, which is 20.

2. Step 2: Evaluate linked list access

   node3.next points to node2, whose value is 20, so node3.next.value is 20.

3. Final Answer:

   20 and 20 -> Option B

4. Quick Check:

   arr[1] = 20, node3.next.value = 20 [OK]

Hint: Array index 1 and linked list next value both give 20 [OK]

Common Mistakes:

• Confusing linked list next pointer direction
• Mixing array indices starting at 0
• Reading node values incorrectly

4. The following code attempts to traverse a linked list and print values, but it causes an error:

function printList(head) {
  let current = head;
  while (current !== null) {
    console.log(current.value);
    current = current.value;
  }
}

const node = { value: 5, next: null };
printList(node);

What is the error and how to fix it?

medium

A. Error: current is undefined; fix by initializing current = head.next;

B. No error; code works fine as is.

C. Error: console.log is incorrect; fix by using console.print instead;

D. Error: current.value is not a node; fix by setting current = current.next;

Solution

1. Step 1: Identify the traversal mistake

   The code sets current = current.value, which is a number, not the next node.

2. Step 2: Correct the pointer update

   To traverse, current should be updated to current.next, the pointer to the next node.

3. Final Answer:

   Error: current.value is not a node; fix by setting current = current.next; -> Option D

4. Quick Check:

   Traverse uses current = current.next [OK]

Hint: Traverse linked list using current = current.next [OK]

Common Mistakes:

• Assigning current = current.value instead of current.next
• Not checking for null before accessing value
• Assuming value holds next node

5. You want to insert a new element at the start of a large collection. Which data structure is more efficient in terms of memory and speed, and why?

hard

A. Linked List, because it allows quick insertion by changing pointers without shifting elements.

B. Both are equally efficient for insertion at start.

C. Array, because it stores elements contiguously and allows fast insertion at start.

D. Depends on the element value and size.

Solution

1. Step 1: Analyze array insertion at start

   Inserting at the start of an array requires shifting all elements, which is slow and uses extra memory temporarily.

2. Step 2: Analyze linked list insertion at start

   Linked list insertion at start only changes the head pointer and new node's next pointer, which is fast and uses minimal extra memory.

3. Final Answer:

   Linked List, because it allows quick insertion by changing pointers without shifting elements. -> Option A

4. Quick Check:

   Linked list insertion at start is faster and memory efficient [OK]

Hint: Linked list inserts at start fast; arrays shift all elements [OK]

Common Mistakes:

• Assuming arrays insert at start quickly
• Ignoring shifting cost in arrays
• Thinking element value affects insertion speed