Traversal of Circular Linked List in DSA C# - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Circular Linked List Traversal

What is the printed output of the following C# code that traverses a circular linked list?

DSA C#

using System;

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

class CircularLinkedList {
    public Node head;

    public void Traverse() {
        if (head == null) return;
        Node temp = head;
        do {
            Console.Write(temp.data + " -> ");
            temp = temp.next;
        } while (temp != head);
        Console.WriteLine("null");
    }
}

class Program {
    static void Main() {
        CircularLinkedList cll = new CircularLinkedList();
        cll.head = new Node(10);
        Node second = new Node(20);
        Node third = new Node(30);
        cll.head.next = second;
        second.next = third;
        third.next = cll.head;
        cll.Traverse();
    }
}

A 10 -> 20 -> null

B 10 -> 20 -> 30 -> null

C 10 -> 20 -> 30 -> 10 -> null

D Runtime error due to infinite loop

💡 Hint

Remember that traversal stops when the node comes back to the head.

The traversal uses a do-while loop that prints nodes until it reaches the head again, so it prints each node once and then stops.

🧠 Conceptual

intermediate

Understanding Circular Linked List Traversal Condition

In a circular linked list traversal, why do we use a do-while loop with the condition 'temp != head' instead of a while loop with 'temp != null'?

A Because temp becomes null immediately in circular lists.

B Because the list is empty and do-while handles empty lists better.

C Because while loops cannot be used with linked lists.

D Because the last node points back to head, so temp never becomes null, and do-while ensures at least one iteration.

💡 Hint

Think about how the last node's next pointer is set in a circular linked list.

In circular linked lists, the last node points back to the head, so temp never becomes null. The do-while loop ensures the traversal runs at least once and stops when temp returns to head.

🔧 Debug

advanced

Identify the Bug in Circular Linked List Traversal

What error will occur when running this traversal code on a circular linked list?

DSA C#

Node temp = head;
while (temp != null) {
    Console.Write(temp.data + " -> ");
    temp = temp.next;
}
Console.WriteLine("null");

A Infinite loop because temp never becomes null in circular linked list

B NullReferenceException because temp is null initially

C Syntax error due to missing braces

D Correct output with all nodes printed once

💡 Hint

Consider what happens to temp in a circular linked list when traversing.

Since the last node points back to head, temp never becomes null, causing an infinite loop.

🚀 Application

advanced

Number of Nodes Traversed in Circular Linked List

Given a circular linked list with 5 nodes, what will be the value of the counter after this traversal code runs?

DSA C#

int count = 0;
Node temp = head;
do {
    count++;
    temp = temp.next;
} while (temp != head);
Console.WriteLine(count);

A 5

B 4

C 6

D Infinite loop, no output

💡 Hint

Each node is counted once until temp returns to head.

The do-while loop counts each node exactly once before temp equals head again, so count equals the number of nodes.

❓ Predict Output

expert

Output of Modified Circular Linked List Traversal with Break

What is the output of this C# code snippet that traverses a circular linked list but breaks early?

DSA C#

Node temp = head;
int steps = 0;
do {
    Console.Write(temp.data + " -> ");
    temp = temp.next;
    steps++;
    if (steps == 2) break;
} while (temp != head);
Console.WriteLine("null");

A Runtime error due to break in do-while

B 10 -> 20 -> 30 -> 10 -> null

C 10 -> 20 -> null

D 10 -> 20 -> 30 -> null

💡 Hint

The loop breaks after printing two nodes.

The loop prints two nodes (10 and 20) then breaks, so output ends with null after those two.

Practice

1. What is the main difference between traversing a circular linked list and a singly linked list?

easy

A. In a circular linked list, traversal stops when the last node's next is null.

B. In a singly linked list, traversal stops when the first node is reached again.

C. In a singly linked list, traversal never ends.

D. In a circular linked list, traversal stops when the starting node is reached again.

Solution

1. Step 1: Understand traversal stopping condition for singly linked list

   Traversal stops when the next pointer is null, indicating the end of the list.

2. Step 2: Understand traversal stopping condition for circular linked list

   Traversal stops when the traversal reaches the starting node again, since the list loops back.

3. Final Answer:

   In a circular linked list, traversal stops when the starting node is reached again. -> Option D

4. Quick Check:

   Circular list stops at start node [OK]

Hint: Remember: circular list loops back to start node [OK]

Common Mistakes:

• Thinking traversal stops at null in circular list
• Confusing stopping conditions of singly and circular lists
• Assuming circular list has a null next pointer

2. Which of the following C# code snippets correctly starts traversal of a circular linked list from the head node?

easy

A. Node current = head; for (int i = 0; i < length; i++) { Console.WriteLine(current.Data); current = current.Next; }

B. Node current = head; while (current != null) { Console.WriteLine(current.Data); current = current.Next; }

C. Node current = head; do { Console.WriteLine(current.Data); current = current.Next; } while (current != head);

D. Node current = head; while (current.Next != null) { Console.WriteLine(current.Data); current = current.Next; }

Solution

1. Step 1: Identify correct loop structure for circular list traversal

   Traversal must use a do-while loop to ensure the head node is processed before checking the condition.

2. Step 2: Check condition to stop traversal

   Traversal stops when current node returns to head, so condition is current != head in while.

3. Final Answer:

   Node current = head; do { Console.WriteLine(current.Data); current = current.Next; } while (current != head); -> Option C

4. Quick Check:

   Use do-while with current != head [OK]

Hint: Use do-while loop to handle circular traversal [OK]

Common Mistakes:

• Using while loop without do causes skipping head node
• Checking for null in circular list causes infinite loop
• Using for loop without length in circular list

3. What will be the output of the following C# code snippet for a circular linked list with nodes containing data 10 -> 20 -> 30 -> (back to 10)?

Node head = new Node(10);
head.Next = new Node(20);
head.Next.Next = new Node(30);
head.Next.Next.Next = head;

Node current = head;
do {
    Console.Write(current.Data + " -> ");
    current = current.Next;
} while (current != head);
Console.WriteLine("null");

medium

A. 10 -> 20 -> 30 -> null

B. 10 -> 20 -> 30 -> 10 -> null

C. 10 -> 20 -> 30 -> 20 -> null

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

Solution

1. Step 1: Understand the circular linked list structure

   The list nodes are 10 -> 20 -> 30, and 30 points back to 10, making it circular.

2. Step 2: Trace the do-while traversal

   Traversal starts at 10, prints 10, moves to 20, prints 20, moves to 30, prints 30, then moves back to 10 which stops the loop.

3. Final Answer:

   10 -> 20 -> 30 -> null -> Option A

4. Quick Check:

   Traversal prints nodes once until back to head [OK]

Hint: Traversal prints nodes once until back to head [OK]

Common Mistakes:

• Printing extra nodes after loop ends
• Confusing circular list with linear list output
• Not stopping traversal at head node

4. Identify the error in the following C# code snippet that attempts to traverse a circular linked list:

Node current = head;
while (current != null) {
    Console.WriteLine(current.Data);
    current = current.Next;
    if (current == head) break;
}

medium

A. The while condition should check current != head instead of current != null.

B. The while condition should be do-while to include head node.

C. The break condition is missing to stop infinite loop.

D. The code will cause a null reference exception.

Solution

1. Step 1: Analyze the while loop condition

   The condition current != null is incorrect for circular linked list because next is never null.

2. Step 2: Identify correct stopping condition

   The loop should stop when current returns to head, so condition should be current != head.

3. Final Answer:

   The while condition should check current != head instead of current != null. -> Option A

4. Quick Check:

   Use current != head to stop traversal [OK]

Hint: Check for current == head, not null, in circular list [OK]

Common Mistakes:

• Using null check in circular list traversal
• Missing break condition causing infinite loop
• Using while instead of do-while causing skipped node

5. Given a circular linked list where each node contains an integer, write a method to find the sum of all node values. Which approach correctly handles the circular nature without infinite looping?

hard

A. Start at head, use while loop with condition current != null, add node data each iteration.

B. Start at head, use do-while loop adding node data, stop when current returns to head.

C. Start at head, use for loop with fixed length equal to number of nodes, add node data.

D. Start at head, use while loop with condition current.Next != null, add node data.

Solution

1. Step 1: Understand circular list traversal for summation

   Traversal must visit each node exactly once and stop when current returns to head to avoid infinite loop.

2. Step 2: Choose correct loop structure

   Using a do-while loop starting at head and stopping when current == head ensures all nodes are included once.

3. Final Answer:

   Start at head, use do-while loop adding node data, stop when current returns to head. -> Option B

4. Quick Check:

   Use do-while and stop at head for sum [OK]

Hint: Use do-while and stop when current == head [OK]

Common Mistakes:

• Using null checks causing infinite loops
• Missing last node in sum due to wrong loop
• Using for loop without knowing list length