Get Length of Linked List in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the length counter to zero.

DSA Javascript

function getLength(head) {
  let length = [1];
  let current = head;
  while (current !== null) {
    length++;
    current = current.next;
  }
  return length;
}

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

Ahead

B1

Cnull

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting length at 1 instead of 0

Initializing length with null or head

The length counter should start at 0 because we haven't counted any nodes yet.

2fill in blank

medium

Complete the code to move to the next node in the linked list.

DSA Javascript

function getLength(head) {
  let length = 0;
  let current = head;
  while (current !== null) {
    length++;
    current = [1];
  }
  return length;
}

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

Acurrent

Bhead.next

Ccurrent.next

Dlength.next

Attempts:

3 left

💡 Hint

Common Mistakes

Using head.next instead of current.next

Assigning current to itself causing infinite loop

To move to the next node, update current to current.next.

3fill in blank

hard

Fix the error in the while loop condition to correctly check the end of the linked list.

DSA Javascript

function getLength(head) {
  let length = 0;
  let current = head;
  while (current [1] null) {
    length++;
    current = current.next;
  }
  return length;
}

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

A!=

B==

C=

D===

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' which assigns instead of compares

Using '==' or '===' which checks equality, not inequality

The loop should continue while current is not null, so use '!='.

4fill in blank

hard

Fill both blanks to create a function that returns the length of a linked list using a for loop.

DSA Javascript

function getLength(head) {
  let length = 0;
  for (let current = head; current [1] null; current = [2]) {
    length++;
  }
  return length;
}

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

A!==

B==

Ccurrent.next

Dhead.next

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of !== in loop condition

Updating current to head.next instead of current.next

The for loop continues while current is not null (using !==), and current moves to current.next each iteration.

5fill in blank

hard

Fill all three blanks to create a recursive function that returns the length of a linked list.

DSA Javascript

function getLength(node) {
  if (node [1] null) {
    return [2];
  } else {
    return 1 + getLength([3]);
  }
}

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

A===

B0

Cnode.next

D!==

Attempts:

3 left

💡 Hint

Common Mistakes

Using != or !== in base case instead of ===

Returning node instead of 0 at base case

Recursing on node instead of node.next

If node is null (=== null), return 0. Otherwise, return 1 plus the length of the rest of the list (node.next).

Practice

1. What does the length of a linked list represent?

easy

A. The memory size of the linked list

B. The value of the first node

C. The number of nodes in the linked list

D. The value of the last node

Solution

1. Step 1: Understand linked list structure

   A linked list is made of nodes connected one after another.

2. Step 2: Define length meaning

   The length counts how many nodes are in the list, regardless of their values.

3. Final Answer:

   The number of nodes in the linked list -> Option C

4. Quick Check:

   Length = number of nodes [OK]

Hint: Length counts nodes, not values or memory size [OK]

Common Mistakes:

• Confusing length with node values
• Thinking length is memory size
• Counting only first or last node

2. Which of the following JavaScript code snippets correctly initializes a variable to count the length of a linked list?

easy

A. let length = 0;

B. let length = null;

C. let length = undefined;

D. let length = '0';

Solution

1. Step 1: Identify correct initialization for counting

   Counting starts from zero, so length should be a number 0.

2. Step 2: Check variable types

   Using null, undefined, or string '0' is incorrect for numeric counting.

3. Final Answer:

   let length = 0; -> Option A

4. Quick Check:

   Initialize count with 0 [OK]

Hint: Start counting from zero using a number variable [OK]

Common Mistakes:

• Using null or undefined instead of 0
• Using string '0' instead of number 0
• Not initializing length variable

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

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

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

let length = 0;
let current = head;
while (current !== null) {
  length++;
  current = current.next;
}
console.log(length);

medium

A. 3

B. 2

C. 1

D. 0

Solution

1. Step 1: Trace linked list nodes

   Nodes are 1 -> 2 -> 3 -> null, so 3 nodes total.

2. Step 2: Count nodes in while loop

   Loop increments length for each node until current is null, so length becomes 3.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Count nodes = 3 [OK]

Hint: Count nodes by traversing until null [OK]

Common Mistakes:

• Stopping loop early
• Not incrementing length
• Incorrectly checking current node

4. Find the error in this code that tries to get the length of a linked list:

function getLength(head) {
  let length = 0;
  let current = head;
  while (current.next !== null) {
    length++;
    current = current.next;
  }
  return length;
}

medium

A. The length variable should start at 1, not 0

B. The loop condition should check current !== null, not current.next !== null

C. The function should return current instead of length

D. The current variable should be initialized to null

Solution

1. Step 1: Analyze loop condition

   Checking current.next !== null misses counting the last node.

2. Step 2: Correct loop condition

   Loop should run while current !== null to count all nodes including last.

3. Final Answer:

   The loop condition should check current !== null, not current.next !== null -> Option B

4. Quick Check:

   Loop until current is null to count all nodes [OK]

Hint: Loop until current is null, not current.next [OK]

Common Mistakes:

• Stopping before last node
• Starting length at 1 incorrectly
• Returning wrong variable

5. Given a linked list where each node has a value and a next pointer, how would you modify the length calculation to skip nodes with value 0 and count only nodes with non-zero values?

hard

A. Count all nodes and then subtract the number of zeros found

B. Skip the first node if its value is 0 before starting the loop

C. Set length to the total nodes minus the number of zeros after counting all nodes

D. Increment length only if current.value !== 0 inside the traversal loop

Solution

1. Step 1: Traverse all nodes

   Loop through each node from head to null as usual.

2. Step 2: Count only non-zero value nodes

   Inside loop, increment length only if current.value !== 0 to skip zeros.

3. Final Answer:

   Increment length only if current.value !== 0 inside the traversal loop -> Option D

4. Quick Check:

   Count nodes with value != 0 during traversal [OK]

Hint: Count nodes only if value is not zero during traversal [OK]

Common Mistakes:

• Skipping nodes incorrectly
• Counting all then subtracting zeros
• Modifying list structure