Why Circular Linked List and Real World Use Cases in DSA Javascript - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a circular linked list node that points to itself.

DSA Javascript

function createNode(value) {
  const node = { value: value, next: null };
  node.next = [1];
  return node;
}

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

Anull

Bundefined

Cnode

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to null breaks the circular link.

Using undefined causes runtime errors.

The node's next pointer should point to itself to form a circular linked list with one node.

2fill in blank

medium

Complete the code to insert a new node after the head in a circular linked list.

DSA Javascript

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

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

Anext

Bprev

Chead

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' causes undefined behavior.

Setting next to head or value breaks the list.

To insert after head, newNode's next should point to head.next.

3fill in blank

hard

Fix the error in the code to correctly traverse a circular linked list once.

DSA Javascript

function traverseCircularList(head) {
  let current = head;
  do {
    console.log(current.value);
    current = current.[1];
  } while (current !== head);
}

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

Anext

Bvalue

Chead

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' causes traversal to fail.

Using 'head' or 'value' as pointer causes runtime errors.

Traversal moves to the next node using the 'next' pointer until it loops back to head.

4fill in blank

hard

Fill both blanks to check if a circular linked list has only one node.

DSA Javascript

function isSingleNode(head) {
  return head !== null && head.[1] === [2];
}

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

Anext

Bprev

Cvalue

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' or 'value' causes incorrect checks.

Comparing different properties leads to wrong results.

In a single-node circular linked list, the node's next points to itself.

5fill in blank

hard

Fill all three blanks to create a function that removes the node after head in a circular linked list.

DSA Javascript

function removeAfterHead(head) {
  if (head === null || head.next === head) return null;
  const removed = head.[1];
  head.[2] = removed.[3];
  return removed;
}

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

Anext

Bprev

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' breaks the list.

Not updating head.next causes the removed node to stay linked.

To remove the node after head, update head.next to removed.next and return removed.

Practice

1. What is a key reason to use a Circular Linked List instead of a regular linked list?

easy

A. It allows continuous traversal without reaching an end

B. It uses less memory than arrays

C. It sorts elements automatically

D. It prevents duplicate values

Solution

1. Step 1: Understand linked list traversal

   Regular linked lists end at a node pointing to null, stopping traversal.

2. Step 2: Analyze circular linked list behavior

   Circular linked lists connect the last node back to the first, enabling endless traversal.

3. Final Answer:

   It allows continuous traversal without reaching an end -> Option A

4. Quick Check:

   Continuous traversal = A [OK]

Hint: Circular lists loop back to start, no end node [OK]

Common Mistakes:

• Confusing memory usage with traversal behavior
• Thinking circular lists sort data automatically
• Assuming circular lists prevent duplicates

2. Which of the following is the correct way to link the last node to the first node in a circular linked list in JavaScript?

easy

A. lastNode.next = null;

B. lastNode.next = firstNode;

C. lastNode = firstNode.next;

D. firstNode.next = lastNode;

Solution

1. Step 1: Identify the circular link requirement

   In a circular linked list, the last node's next pointer must point to the first node.

2. Step 2: Match code to requirement

   Setting lastNode.next = firstNode; creates the circular link.

3. Final Answer:

   lastNode.next = firstNode; -> Option B

4. Quick Check:

   Last node points to first node = D [OK]

Hint: Last node's next points to first node for circular link [OK]

Common Mistakes:

• Setting lastNode.next to null breaks circularity
• Confusing assignment direction between nodes
• Linking firstNode.next to lastNode instead

3. Consider this JavaScript code snippet for a circular linked list traversal:

let current = head;
do { console.log(current.value); current = current.next; } while (current !== head);

What will be the output if the list has nodes with values 10, 20, 30 linked circularly?

medium

A. 10 20 30

B. 10 20 30 10 20 30 ... (infinite loop)

C. 10 20 30 null

D. Syntax error

Solution

1. Step 1: Understand the do-while loop condition

   The loop prints current.value and moves to next node until current equals head again.

2. Step 2: Trace the traversal

   Starting at head (10), it prints 10, then 20, then 30. When current.next is head again, loop stops.

3. Final Answer:

   10 20 30 -> Option A

4. Quick Check:

   Print each node once until back to head = B [OK]

Hint: do-while stops when current returns to head [OK]

Common Mistakes:

• Assuming infinite loop without condition check
• Expecting null at end in circular list
• Confusing do-while with while loop behavior

4. The following code attempts to create a circular linked list but causes an infinite loop when traversed. What is the error?

function createCircularList(values) {
  let head = { value: values[0], next: null };
  let current = head;
  for (let i = 1; i < values.length; i++) {
    current.next = { value: values[i], next: null };
    current = current.next;
  }
  // Missing circular link here
  return head;
}

medium

A. The list nodes are not linked at all

B. The head node is null

C. The for loop has wrong index range

D. The last node's next is not linked back to head

Solution

1. Step 1: Review list creation logic

   Nodes are linked sequentially but last node's next remains null.

2. Step 2: Identify missing circular link

   Without linking last node's next to head, traversal expecting circularity causes infinite loop.

3. Final Answer:

   The last node's next is not linked back to head -> Option D

4. Quick Check:

   Missing circular link causes infinite loop = C [OK]

Hint: Always link last node back to head for circular list [OK]

Common Mistakes:

• Assuming nodes are not linked at all
• Thinking head is null without checking
• Misreading for loop index range

5. Which real-world scenario best fits the use of a circular linked list?

hard

A. Sorting numbers in ascending order

B. Storing user data in a database table

C. Implementing a music playlist that repeats songs endlessly

D. Searching for a value in a binary tree

Solution

1. Step 1: Understand circular linked list use cases

   Circular linked lists are ideal for repeated cycles without stopping, like playlists.

2. Step 2: Match options to use cases

   Music playlists that loop songs fit circular lists; other options relate to different data structures.

3. Final Answer:

   Implementing a music playlist that repeats songs endlessly -> Option C

4. Quick Check:

   Endless looping playlist = A [OK]

Hint: Circular lists suit repeated cycles like playlists [OK]

Common Mistakes:

• Confusing circular lists with sorting or searching structures
• Choosing database storage as circular list use
• Ignoring the repeat cycle requirement