Insert at Beginning of Circular Linked List in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new node with the given value.

DSA Javascript

function Node(value) {
  this.data = [1];
  this.next = null;
}

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

Avalue

Bnext

Cdata

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'next' instead of 'value' for data.

Setting data to null instead of the value.

The new node's data should be set to the given value parameter.

2fill in blank

medium

Complete the code to handle the case when the list is empty (head is null).

DSA Javascript

if (head === null) {
  newNode.next = [1];
  head = newNode;
  return head;
}

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

AnewNode

Bhead

Cundefined

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to null breaks the circular property.

Setting next to head when head is null causes errors.

In a circular linked list with one node, the node points to itself.

3fill in blank

hard

Fix the error in the loop that finds the last node in the circular linked list.

DSA Javascript

let current = head;
while (current.next !== [1]) {
  current = current.next;
}

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

AnewNode

Bhead

Cnull

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for null instead of head causes infinite loops.

Using newNode instead of head in the condition.

The last node points back to head in a circular linked list.

4fill in blank

hard

Fill both blanks to insert the new node at the beginning and update the last node's next pointer.

DSA Javascript

current.next = [1];
newNode.next = [2];
return newNode;

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

AnewNode

Bhead

Ccurrent

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Setting newNode.next to current instead of head.

Not updating current.next to newNode.

The last node's next should point to the newNode, and newNode.next should point to the old head.

5fill in blank

hard

Fill all three blanks to complete the insertAtBeginning function for a circular linked list.

DSA Javascript

function insertAtBeginning(head, value) {
  const newNode = new Node([1]);
  if (head === null) {
    newNode.next = [2];
    return newNode;
  }
  let current = head;
  while (current.next !== [3]) {
    current = current.next;
  }
  current.next = newNode;
  newNode.next = head;
  return newNode;
}

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

Avalue

BnewNode

Chead

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Not setting newNode.next to itself when list is empty.

Incorrect loop condition to find last node.

The new node is created with value, points to itself if list is empty, and the last node points to head.

Practice

1. What happens when you insert a new node at the beginning of a circular linked list?

easy

A. The new node becomes the head and points to the old head, maintaining the circular link.

B. The new node is added at the end, breaking the circular link.

C. The new node replaces the last node in the list.

D. The list becomes linear instead of circular.

Solution

1. Step 1: Understand the circular linked list structure

   In a circular linked list, the last node points back to the head node, forming a circle.

2. Step 2: Insert new node at beginning

   The new node is linked to the current head, and the last node's next pointer is updated to this new node, making it the new head.

3. Final Answer:

   The new node becomes the head and points to the old head, maintaining the circular link. -> Option A

4. Quick Check:

   New head points to old head, circle intact [OK]

Hint: New head points to old head; last node points to new head [OK]

Common Mistakes:

• Forgetting to update last node's next pointer
• Breaking the circular link by not linking last node to new head
• Inserting at end instead of beginning

2. Which of the following is the correct syntax to create a new node and insert it at the beginning of a circular linked list in JavaScript?

easy

A. const newNode = { data: value, next: head }; last.next = newNode; head = newNode;

B. const newNode = { data: value, next: null }; last.next = head; head = newNode;

C. const newNode = { data: value, next: head }; head.next = newNode; head = newNode;

D. const newNode = { data: value, next: null }; newNode.next = head; head = newNode;

Solution

1. Step 1: Create new node with next pointing to current head

   The new node's next should point to the current head to insert at beginning.

2. Step 2: Update last node's next to new node and update head

   Since it's circular, last node's next must point to new node, then head is updated to new node.

3. Final Answer:

   const newNode = { data: value, next: head }; last.next = newNode; head = newNode; -> Option A

4. Quick Check:

   New node next = head, last.next = new node, head updated [OK]

Hint: New node next = head; last.next = new node; update head [OK]

Common Mistakes:

• Not updating last.next to new node
• Setting newNode.next to null instead of head
• Updating head before last.next

3. What will be the output of the following code snippet after inserting 10 at the beginning of the circular linked list?

function Node(data) { this.data = data; this.next = null; }

let head = new Node(20);
let second = new Node(30);
head.next = second;
second.next = head; // circular link

// Insert 10 at beginning
const newNode = new Node(10);
newNode.next = head;
second.next = newNode;
head = newNode;

// Print list starting from head
let temp = head;
do {
  console.log(temp.data);
  temp = temp.next;
} while(temp !== head);

medium

A. 20 30 10

B. 10 20 30

C. 10 30 20

D. 30 20 10

Solution

1. Step 1: Understand the initial circular list

   Initially, list is 20 -> 30 -> back to 20.

2. Step 2: Insert 10 at beginning and update links

   New node 10 points to 20 (old head), 30 (last node) points to 10, head updated to 10.

3. Step 3: Print order starting from new head

   Traversal prints 10, then 20, then 30, then stops as it loops back to head.

4. Final Answer:

   10 20 30 -> Option B

5. Quick Check:

   New head 10, then 20, then 30 [OK]

Hint: New head data prints first, then follow next pointers [OK]

Common Mistakes:

• Not updating last node's next to new head
• Printing nodes until null instead of circular condition
• Confusing node order after insertion

4. Identify the error in the following code that inserts a node at the beginning of a circular linked list:

function insertAtBeginning(head, value) {
  const newNode = { data: value, next: head };
  let temp = head;
  while(temp.next !== null) {
    temp = temp.next;
  }
  temp.next = newNode;
  head = newNode;
  return head;
}

medium

A. The function should not return head.

B. The newNode's next should be null, not head.

C. The head should not be updated after insertion.

D. The while loop condition should check for temp.next !== head instead of null.

Solution

1. Step 1: Analyze loop condition for circular list

   In a circular linked list, last node's next points to head, not null, so loop should check temp.next !== head.

2. Step 2: Understand impact of wrong condition

   Checking for null causes infinite loop or error because next is never null in circular list.

3. Final Answer:

   The while loop condition should check for temp.next !== head instead of null. -> Option D

4. Quick Check:

   Loop until last node points to head [OK]

Hint: In circular list, last.next points to head, not null [OK]

Common Mistakes:

• Using null check in circular list traversal
• Not updating last node's next pointer correctly
• Forgetting to update head after insertion

5. You have a circular linked list with nodes containing values 5, 15, and 25. You want to insert a new node with value 10 at the beginning. After insertion, what will be the correct order of nodes when traversed starting from the new head, and why is updating the last node's next pointer essential?

hard

A. 5 -> 15 -> 25 -> 10; last.next should point to old head, not new node.

B. 10 -> 5 -> 15 -> 25; updating last.next is optional since newNode.next points to head.

C. 10 -> 5 -> 15 -> 25; updating last.next maintains the circular link to new head.

D. 10 -> 15 -> 25 -> 5; last.next should point to newNode.next.

Solution

1. Step 1: Insert new node at beginning and update pointers

   New node 10 points to old head 5; last node 25 must point to new node 10 to keep circular link.

2. Step 2: Traverse list from new head

   Traversal order is 10 -> 5 -> 15 -> 25, then back to 10.

3. Step 3: Importance of updating last.next

   If last.next is not updated to new head, circular link breaks and traversal fails.

4. Final Answer:

   10 -> 5 -> 15 -> 25; updating last.next maintains the circular link to new head. -> Option C

5. Quick Check:

   Last node points to new head to keep circle [OK]

Hint: Last node must point to new head to keep circle intact [OK]

Common Mistakes:

• Skipping update of last.next pointer
• Assuming newNode.next update is enough
• Incorrect traversal order after insertion