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

Insert at End of Circular Linked List

📖 Scenario: You are managing a circular queue of tasks where the last task points back to the first task, forming a circle. You want to add a new task at the end of this circular list.

🎯 Goal: Build a circular linked list and write code to insert a new node at the end of the list.

📋 What You'll Learn

Create a Node class with an integer data and a next pointer

Create a circular linked list with three nodes containing data 10, 20, and 30

Create a method to insert a new node at the end of the circular linked list

Insert a new node with data 40 at the end

Print the circular linked list starting from the head node

💡 Why This Matters

🌍 Real World

Circular linked lists are useful in real-world scenarios like task scheduling, where tasks repeat in a cycle.

💼 Career

Understanding circular linked lists helps in roles involving system programming, embedded systems, and designing efficient data structures.

1

Create the Circular Linked List Nodes

Create a class called Node with an integer data and a Node next pointer. Then create three nodes with data 10, 20, and 30. Link them so that the last node points back to the first node to form a circular linked list. Store the first node in a variable called head.

DSA C#

// Define Node class and create circular linked list with nodes 10, 20, 30
// Your code here

Hint

Remember to make the last node point back to the first node to form a circle.

2

Create a Method to Insert at End

Create a method called InsertAtEnd that takes two parameters: Node head and int data. This method should create a new node with the given data and insert it at the end of the circular linked list. The method should return the head of the updated list.

DSA C#

public class Node
{
    public int data;
    public Node next;
    public Node(int data)
    {
        this.data = data;
        this.next = null;
    }
}

Node head = new Node(10);
Node second = new Node(20);
Node third = new Node(30);
head.next = second;
second.next = third;
third.next = head; // Circular link

// Create InsertAtEnd method below
// Your code here

Hint

Traverse the list until you find the last node (which points back to head), then insert the new node after it.

3

Insert a New Node with Data 40 at the End

Call the InsertAtEnd method with head and 40 to insert a new node with data 40 at the end of the circular linked list. Update the head variable with the returned value.

DSA C#

public class Node
{
    public int data;
    public Node next;
    public Node(int data)
    {
        this.data = data;
        this.next = null;
    }
}

Node head = new Node(10);
Node second = new Node(20);
Node third = new Node(30);
head.next = second;
second.next = third;
third.next = head; // Circular link

Node InsertAtEnd(Node head, int data)
{
    Node newNode = new Node(data);
    if (head == null)
    {
        newNode.next = newNode;
        return newNode;
    }
    Node temp = head;
    while (temp.next != head)
    {
        temp = temp.next;
    }
    temp.next = newNode;
    newNode.next = head;
    return head;
}

// Insert node with data 40 at the end
// Your code here

Hint

Assign the result of InsertAtEnd(head, 40) back to head.

4

Print the Circular Linked List

Write a PrintList method that takes Node head and prints the data of each node in the circular linked list separated by arrows ->. Then call PrintList(head) to display the list.

DSA C#

public class Node
{
    public int data;
    public Node next;
    public Node(int data)
    {
        this.data = data;
        this.next = null;
    }
}

Node head = new Node(10);
Node second = new Node(20);
Node third = new Node(30);
head.next = second;
second.next = third;
third.next = head; // Circular link

Node InsertAtEnd(Node head, int data)
{
    Node newNode = new Node(data);
    if (head == null)
    {
        newNode.next = newNode;
        return newNode;
    }
    Node temp = head;
    while (temp.next != head)
    {
        temp = temp.next;
    }
    temp.next = newNode;
    newNode.next = head;
    return head;
}

head = InsertAtEnd(head, 40);

// Write PrintList method and call it
// Your code here

Hint

Use a do-while loop to print nodes until you reach the head again.

Practice

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

easy

A. The new node points back to the head, maintaining the circular structure.

B. The new node points to null, breaking the circular structure.

C. The new node becomes the head and points to null.

D. The new node is inserted at the beginning, not the end.

Solution

1. Step 1: Understand circular linked list structure

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

2. Step 2: Insert new node at the end

   The new node is linked after the current last node, and its next pointer is set to the head, preserving the circle.

3. Final Answer:

   The new node points back to the head, maintaining the circular structure. -> Option A

4. Quick Check:

   New node next = head keeps list circular [OK]

Hint: New end node must link to head to keep circle [OK]

Common Mistakes:

• Setting new node's next to null breaks the circle
• Inserting new node at head instead of end
• Forgetting to update last node's next pointer

2. Which of the following C# code snippets correctly inserts a new node at the end of a circular linked list?

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 = head.next; lastNode.next = head;

Solution

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

   To maintain circularity, newNode.next must point to head node.

2. Step 2: Link last node to new node

   Update lastNode.next to newNode to insert at 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 = head; last node next = new node [OK]

Common Mistakes:

• Setting new node next to null breaks circle
• Linking new node to last node instead of head
• Not updating last node's next pointer

3. Given the circular linked list: 10 -> 20 -> 30 -> back to 10, what is the list after inserting 40 at the end?

medium

A. 40 -> 10 -> 20 -> 30 -> back to 40

B. 10 -> 20 -> 30 -> back to 40

C. 10 -> 20 -> 30 -> 40 -> back to 10

D. 10 -> 20 -> 30 -> 40 -> null

Solution

1. Step 1: Identify current circular list

   List is 10 -> 20 -> 30, last node 30 points back to 10.

2. Step 2: Insert 40 at end

   New node 40 is linked after 30, and 40 points back to 10 to keep circle.

3. Final Answer:

   10 -> 20 -> 30 -> 40 -> back to 10 -> Option C

4. Quick Check:

   New node added at end, circle maintained [OK]

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

Common Mistakes:

• Making new node head instead of last
• Breaking circle by pointing new node to null
• Forgetting to update last node's next pointer

4. What is wrong with this code snippet for inserting at the end of a circular linked list?

newNode.next = null;
lastNode.next = newNode;
newNode.next = head;

medium

A. The code correctly inserts the node without issues.

B. Setting newNode.next to null breaks the circular link temporarily.

C. newNode.next should point to lastNode, not head.

D. lastNode.next should not be updated before newNode.next.

Solution

1. Step 1: Analyze newNode.next assignment

   Setting newNode.next = null breaks the circular link temporarily, which is unnecessary.

2. Step 2: Check order of pointer updates

   Correct insertion requires newNode.next to point to head immediately to maintain circle.

3. Final Answer:

   Setting newNode.next to null breaks the circular link temporarily. -> Option B

4. Quick Check:

   newNode.next must never be null in circular list [OK]

Hint: Never set new node's next to null in circular list [OK]

Common Mistakes:

• Assigning null to newNode.next
• Updating lastNode.next before setting newNode.next
• Confusing pointer directions

5. You have a circular linked list with only one node (value 5) pointing to itself. After inserting a new node with value 10 at the end, what is the correct structure?

hard

A. 5 -> 10 -> null

B. 5 -> back to 10 -> back to 5

C. 10 -> 5 -> back to 10

D. 5 -> 10 -> back to 5

Solution

1. Step 1: Understand single-node circular list

   Initially, node 5 points to itself, forming a circle.

2. Step 2: Insert new node 10 at end

   New node 10 is linked after 5, and 10 points back to 5 to maintain circularity.

3. Final Answer:

   5 -> 10 -> back to 5 -> Option D

4. Quick Check:

   Two nodes linked circularly, last points to head [OK]

Hint: New node next = head even if list has one node [OK]

Common Mistakes:

• Pointing new node to null instead of head
• Not updating original node's next pointer
• Confusing order of nodes after insertion