Insert at End of Circular Linked List in DSA Javascript - Build from Scratch

Insert at End of Circular Linked List

📖 Scenario: You are managing a circular linked list that represents a round-robin queue of tasks. Each node holds a task number. You want to add a new task at the end of this circular list.

🎯 Goal: Build a circular linked list with initial tasks, then write code to insert a new task at the end, and finally print the list to verify the insertion.

📋 What You'll Learn

Create a circular linked list with three nodes having values 10, 20, and 30.

Create a variable called newNode with value 40 to insert at the end.

Write code to insert newNode at the end of the circular linked list.

Print the circular linked list starting from the head node, showing all nodes once.

💡 Why This Matters

🌍 Real World

Circular linked lists are used in real-world systems like task schedulers, multiplayer games, and music playlists where the list loops continuously.

💼 Career

Understanding circular linked lists helps in roles involving system design, embedded systems, and software development where efficient cyclic data handling is needed.

1

Create the initial circular linked list

Create three nodes called node1, node2, and node3 with values 10, 20, and 30 respectively. Link them in a circular way so that node3.next points back to node1. Also create a variable head pointing to node1.

DSA Javascript

// Your code here to create nodes and link them circularly

Hint

Remember to create nodes with new Node(value) and link their next pointers to form a circle.

2

Create the new node to insert

Create a new node called newNode with value 40 that you will insert at the end of the circular linked list.

DSA Javascript

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

const node1 = new Node(10);
const node2 = new Node(20);
const node3 = new Node(30);

node1.next = node2;
node2.next = node3;
node3.next = node1;

const head = node1;

// Create newNode with value 40
// Your code here

Hint

Use const newNode = new Node(40); to create the new node.

3

Insert the new node at the end of the circular linked list

Write code to insert newNode at the end of the circular linked list. Traverse the list starting from head to find the last node (the node whose next points back to head). Then update the last node's next to newNode and newNode.next to head.

DSA Javascript

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

const node1 = new Node(10);
const node2 = new Node(20);
const node3 = new Node(30);

node1.next = node2;
node2.next = node3;
node3.next = node1;

const head = node1;

const newNode = new Node(40);

// Insert newNode at the end of the circular linked list
// Your code here

Hint

Use a while loop to find the last node, then update pointers to insert newNode.

4

Print the circular linked list

Write code to print the values of the circular linked list starting from head. Traverse the list and print each node's value separated by -> . Stop after printing all nodes once (when you reach head again).

DSA Javascript

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

const node1 = new Node(10);
const node2 = new Node(20);
const node3 = new Node(30);

node1.next = node2;
node2.next = node3;
node3.next = node1;

const head = node1;

const newNode = new Node(40);

let current = head;
while (current.next !== head) {
    current = current.next;
}
current.next = newNode;
newNode.next = head;

// Print the circular linked list values
// Your code here

Hint

Use a do...while loop to print all nodes once, then add 'null' at the end.

Practice

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

easy

A. The new node points to itself, becoming the only node in the list.

B. The new node points to null, ending the list.

C. The list remains empty because no insertion is possible.

D. The new node points to the head, but the list is not circular.

Solution

1. Step 1: Understand empty circular linked list

   An empty circular linked list has no nodes, so inserting the first node means it must point to itself to maintain circularity.

2. Step 2: Insert new node and set its next pointer

   The new node's next pointer is set to itself, making it the only node and forming a circular link.

3. Final Answer:

   The new node points to itself, becoming the only node in the list. -> Option A

4. Quick Check:

   Empty list insertion = node points to itself [OK]

Hint: First node in circular list points to itself [OK]

Common Mistakes:

• Setting next pointer to null instead of itself
• Assuming list remains empty after insertion
• Not maintaining circular link for single node

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

easy

A. newNode.next = head; lastNode.next = newNode;

B. newNode.next = null; lastNode.next = newNode;

C. newNode.next = lastNode; head.next = newNode;

D. newNode.next = newNode; head = newNode;

Solution

1. Step 1: Set new node's next to head

   In a circular linked list, the last node points to the head, so newNode.next must point to head to maintain circularity.

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

   The current last node's next pointer is updated to newNode, inserting it at the end.

3. Final Answer:

   newNode.next = head; lastNode.next = newNode; -> Option A

4. Quick Check:

   New node points to head, last node points to new node [OK]

Hint: New node next points to head, last node next points to new node [OK]

Common Mistakes:

• Setting newNode.next to null breaks circularity
• Swapping pointers incorrectly
• Not updating last node's next pointer

3. What will be the printed circular linked list after inserting a node with value 4 at the end of the list: 1 -> 2 -> 3 -> (back to 1)?

medium

A. 4 -> 1 -> 2 -> 3 -> (back to 4)

B. 1 -> 2 -> 3 -> 4 -> (back to 1)

C. 1 -> 2 -> 3 -> (back to 4)

D. 1 -> 2 -> 3 -> 4 -> null

Solution

1. Step 1: Identify current list structure

   The list currently has nodes 1, 2, 3 linked circularly, so last node 3 points back to 1.

2. Step 2: Insert node with value 4 at end

   New node 4's next points to head (1), and node 3's next points to node 4, extending the circle.

3. Final Answer:

   1 -> 2 -> 3 -> 4 -> (back to 1) -> Option B

4. Quick Check:

   New node added at end, circle maintained [OK]

Hint: New node added after last, points to head [OK]

Common Mistakes:

• Placing new node at start instead of end
• Breaking circular link by pointing to null
• Incorrectly updating pointers causing broken list

4. Given the code snippet below, what is the error when inserting at the end of a circular linked list?

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

medium

A. Head is not updated when list is empty.

B. The while loop condition is incorrect and causes infinite loop.

C. New node is not created properly.

D. New node's next is not set to head, breaking circularity.

Solution

1. Step 1: Check new node's next pointer

   New node's next is initialized to null and never updated to point to head, breaking the circular link.

2. Step 2: Verify circularity after insertion

   Since temp.next points to newNode but newNode.next is null, the list is no longer circular.

3. Final Answer:

   New node's next is not set to head, breaking circularity. -> Option D

4. Quick Check:

   New node next must point to head [OK]

Hint: Always set new node's next to head in circular list [OK]

Common Mistakes:

• Forgetting to link new node back to head
• Incorrect loop condition causing infinite loop
• Not handling empty list properly

5. You have a circular linked list with nodes 10 -> 20 -> 30 -> (back to 10). You want to insert a new node with value 40 at the end, but also keep the list sorted in ascending order. Which approach correctly inserts the node and maintains circularity and order?

hard

A. Insert 40 at the end as usual, then rotate the list to start at 40.

B. Insert 40 at the head and update last node's next to new node.

C. Traverse to find correct position for 40, insert it there, update pointers to keep circularity.

D. Insert 40 at the end and break circularity temporarily.

Solution

1. Step 1: Find correct sorted position for new node

   Traverse the list to find where 40 fits between nodes to keep ascending order.

2. Step 2: Insert new node at found position and update pointers

   Insert new node between nodes, update previous node's next to new node, and new node's next to next node, maintaining circularity.

3. Final Answer:

   Traverse to find correct position for 40, insert it there, update pointers to keep circularity. -> Option C

4. Quick Check:

   Sorted insert requires correct position and pointer updates [OK]

Hint: Insert in sorted order by finding correct spot, update pointers [OK]

Common Mistakes:

• Inserting at end without sorting
• Breaking circularity during insertion
• Not updating last node's next pointer correctly