Why Circular Linked List and Real World Use Cases in DSA C# - 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 C#

Node node = new Node(10);
node.next = [1];

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

Anode

Bnew Node(10)

Chead

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Setting next to null breaks the circular property.

Creating a new node instead of pointing to the existing one.

In a circular linked list, the last node points back to the first node or itself if it's the only node. Here, setting node.next = node makes it circular.

2fill in blank

medium

Complete the code to traverse a circular linked list starting from head and stop after one full cycle.

DSA C#

Node current = head;
do {
    Console.WriteLine(current.data);
    current = [1];
} while (current != head);

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

Acurrent.prev

Bhead

Ccurrent.next

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using null instead of current.next causes errors.

Using current.prev moves backward, not forward.

To move through the circular linked list, we update current to current.next each time until we return to head.

3fill in blank

hard

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

DSA C#

Node newNode = new Node(20);
newNode.next = head.next;
head.next = [1];

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

Ahead.next

Bhead

Cnull

DnewNode

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning head.next to head creates a loop without the new node.

Assigning head.next to null breaks the list.

To insert the new node after head, head.next must point to newNode.

4fill in blank

hard

Fill both blanks to complete the method that checks if a circular linked list contains a value.

DSA C#

public bool Contains(Node head, int value) {
    if (head == null) return false;
    Node current = head;
    do {
        if (current.data [1] value) return true;
        current = current.[2];
    } while (current != head);
    return false;
}

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

A==

B!=

Cnext

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using != instead of == causes wrong condition.

Using prev moves backward, not forward.

The method compares each node's data to the value using == and moves forward using next until it loops back to head.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps node data to its next node's data in a circular linked list.

DSA C#

var map = new Dictionary<int, int>();
Node current = head;
do {
    map[[1]] = current.[2].[3];
    current = current.next;
} while (current != head);

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

Acurrent.data

Bnext

Cdata

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using head instead of current for keys.

Accessing next node incorrectly.

This code maps each node's data to the data of its next node by accessing current.data as key and current.next.data as value.

Practice

1. What is the main advantage of using a Circular Linked List over a regular singly linked list?

easy

A. It allows continuous traversal from any node without reaching a null end.

B. It uses less memory than a singly linked list.

C. It automatically sorts the elements.

D. It prevents duplicate elements.

Solution

1. Step 1: Understand the structure of circular linked list

   A circular linked list connects the last node back to the first node, forming a circle.

2. Step 2: Compare traversal behavior

   This structure allows traversal to continue indefinitely from any node without hitting a null pointer.

3. Final Answer:

   It allows continuous traversal from any node without reaching a null end. -> Option A

4. Quick Check:

   Continuous traversal = Advantage of circular linked list [OK]

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

Common Mistakes:

• Thinking circular lists save memory
• Assuming circular lists sort data automatically
• Believing circular lists prevent duplicates

2. Which of the following is the correct way to check if a circular linked list has only one node in C#?

easy

A. if (head != null && head.Next == head)

B. if (head.Next == null)

C. if (head == null)

D. if (head != null && head.Next == null)

Solution

1. Step 1: Understand single node condition in circular list

   In a circular linked list, a single node points to itself, so head.Next equals head.

2. Step 2: Identify correct condition

   The condition head != null && head.Next == head correctly checks for one node.

3. Final Answer:

   if (head != null && head.Next == head) -> Option A

4. Quick Check:

   Single node points to itself = Condition D [OK]

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

Common Mistakes:

• Checking for null next in circular list
• Confusing singly linked list condition with circular
• Ignoring null head check

3. Consider the following C# code snippet for a circular linked list traversal:

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

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

medium

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

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

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

D. null

Solution

1. Step 1: Understand the traversal loop

   The loop starts at head and prints data, then moves to next node until it reaches head again.

2. Step 2: Trace the output for nodes 10, 20, 30

   It prints 10, then 20, then 30, then stops because current equals head again.

3. Final Answer:

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

4. Quick Check:

   One full circle traversal = Output B [OK]

Hint: Loop stops when current returns to head [OK]

Common Mistakes:

• Thinking loop prints infinitely
• Printing extra nodes after full circle
• Missing the null at the end

4. The following code snippet is intended to insert a new node with data 40 at the end of a circular linked list. What is the error?

Node newNode = new Node(40);
Node temp = head;
while (temp.Next != null) {
    temp = temp.Next;
}
temp.Next = newNode;
newNode.Next = head;

medium

A. There is no error; the code works correctly.

B. The newNode.Next should be set to null, not head.

C. The newNode should be inserted at the beginning, not the end.

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

Solution

1. Step 1: Analyze loop condition in circular list

   In a circular linked list, last node's Next points to head, never null.

2. Step 2: Identify correct loop condition

   The loop should stop when temp.Next equals head, not null, to find last node.

3. Final Answer:

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

4. Quick Check:

   Loop condition must detect circular end = The while loop condition should check for temp.Next != head instead of null. [OK]

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

Common Mistakes:

• Using null check in circular list traversal
• Setting newNode.Next to null
• Misplacing new node at start instead of end

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

hard

A. Storing user login history in chronological order.

B. Implementing a music playlist that loops songs continuously.

C. Maintaining a sorted list of student grades.

D. Implementing a stack data structure.

Solution

1. Step 1: Understand circular linked list use cases

   Circular linked lists are ideal when data needs to be accessed repeatedly in a loop without stopping.

2. Step 2: Match scenario to circular list behavior

   A music playlist that loops songs continuously fits perfectly as it cycles through songs endlessly.

3. Final Answer:

   Implementing a music playlist that loops songs continuously. -> Option B

4. Quick Check:

   Continuous looping = Music playlist use case [OK]

Hint: Looping playlists = circular linked list use [OK]

Common Mistakes:

• Choosing sorted list for circular list
• Confusing stack with circular list
• Selecting login history which is linear