Create a Circular Singly Linked List in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA C#

Node newNode = new Node([1]);

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

Anode

Bvalue

Cnull

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'node' instead of 'value' as the argument.

Passing 'null' which creates an empty node.

Using 'next' which is a pointer, not the value.

The new node should be created with the given value variable.

2fill in blank

medium

Complete the code to make the new node point to itself, forming a circular link.

DSA C#

newNode.[1] = newNode;

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

Anext

Bprev

Cvalue

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is not used in singly linked lists.

Assigning 'value' which is data, not a pointer.

Assigning 'head' which is a reference to the list start.

In a circular singly linked list, the 'next' pointer of the new node points to itself.

3fill in blank

hard

Fix the error in the code to update the last node's next pointer to the new node.

DSA C#

last.[1] = newNode;

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

Anext

Bvalue

Cprev

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'value' which is data, not a pointer.

Using 'prev' which is not part of singly linked lists.

Assigning 'head' which is the start node, not the pointer.

The 'next' pointer of the last node should point to the new node to maintain the circular link.

4fill in blank

hard

Fill both blanks to update the new node's next pointer and the list's head pointer.

DSA C#

newNode.[1] = head;
head = [2];

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

Anext

BnewNode

Clast

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is not used here.

Assigning 'last' to head which is incorrect.

Not updating the head pointer.

The new node's next points to the current head, and then head is updated to the new node.

5fill in blank

hard

Fill all three blanks to complete the insertion of a new node in the circular singly linked list.

DSA C#

Node newNode = new Node([1]);
newNode.[2] = head;
last.[3] = newNode;

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

Avalue

Bnext

Cprev

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is not part of singly linked lists.

Not linking last.next to newNode.

Not setting newNode.next to head.

Create new node with value, set newNode.next to head, and last.next to newNode to insert correctly.

Practice

1. What is the key difference between a circular singly linked list and a regular singly linked list?

easy

A. The last node points to null in a circular singly linked list.

B. Nodes have two pointers in a circular singly linked list.

C. The last node points back to the first node in a circular singly linked list.

D. Nodes are stored in an array in a circular singly linked list.

Solution

1. Step 1: Understand the node connection in a regular singly linked list

   In a regular singly linked list, the last node's next pointer is null, marking the end.

2. Step 2: Understand the node connection in a circular singly linked list

   In a circular singly linked list, the last node's next pointer points back to the first node, forming a circle.

3. Final Answer:

   The last node points back to the first node in a circular singly linked list. -> Option C

4. Quick Check:

   Last node next = first node in circular list [OK]

Hint: Remember: circular means last node loops to first [OK]

Common Mistakes:

• Thinking last node points to null in circular list
• Confusing circular with doubly linked list
• Assuming nodes have two pointers in circular singly linked list

2. Which of the following is the correct way to initialize a circular singly linked list with one node in C#?

easy

A. Node head = new Node(5); head.next = head;

B. Node head = new Node(5); head.next = null;

C. Node head = null; head.next = head;

D. Node head = new Node(5); head = null;

Solution

1. Step 1: Create a new node with value 5

   Node head = new Node(5); creates a node with data 5.

2. Step 2: Point the node's next to itself to form a circular link

   head.next = head; makes the list circular with one node.

3. Final Answer:

   Node head = new Node(5); head.next = head; -> Option A

4. Quick Check:

   Single node next points to itself [OK]

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

Common Mistakes:

• Setting next to null instead of self
• Assigning null to head after creation
• Trying to set next on a null head

3. What will be the output of the following code snippet that creates a circular singly linked list with nodes 1, 2, 3 and prints them once?

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

Node head = new Node(1);
Node second = new Node(2);
Node third = new Node(3);
head.next = second;
second.next = third;
third.next = head; // circular link

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

medium

A. 1 -> 2 -> null

B. 1 -> 2 -> 3 -> 1 -> 2 -> 3 -> null

C. 1 -> 2 -> 3 -> 3 -> null

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

Solution

1. Step 1: Create nodes and link them circularly

   Nodes 1, 2, 3 are linked so that third.next points back to head, forming a circle.

2. Step 2: Traverse and print nodes once using do-while loop

   The loop prints data starting at head and stops when temp returns to head, printing 1, 2, 3 once.

3. Final Answer:

   1 -> 2 -> 3 -> null -> Option D

4. Quick Check:

   Loop prints each node once before stopping [OK]

Hint: do-while stops after one full circle [OK]

Common Mistakes:

• Using while loop without do causes skipping first node
• Printing nodes infinitely without stop condition
• Confusing circular list with linear list output

4. Identify the error in this code snippet that tries to insert a new node with value 4 at the end of a circular singly linked list:

Node newNode = new Node(4);
Node temp = head;
while (temp.next != null) {
  temp = temp.next;
}
temp.next = newNode;
newNode.next = head;

medium

A. newNode.next should be null, not head.

B. The while loop condition should check for temp.next != head, not null.

C. temp should be initialized to null before the loop.

D. The newNode should be created after the loop.

Solution

1. Step 1: Understand circular list's last node pointer

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

2. Step 2: Correct the loop condition to find last node

   The loop should check temp.next != head to stop at the last node, not temp.next != null.

3. Final Answer:

   The while loop condition should check for temp.next != head, not null. -> Option B

4. Quick Check:

   Last node next = head, not 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 breaking circularity
• Initializing temp incorrectly

5. You want to create a circular singly linked list from an array of integers [10, 20, 30, 40]. Which approach correctly creates the circular list and returns the head node?

public Node CreateCircularList(int[] arr) {
  if (arr.Length == 0) return null;
  Node head = new Node(arr[0]);
  Node current = head;
  for (int i = 1; i < arr.Length; i++) {
    current.next = new Node(arr[i]);
    current = current.next;
  }
  // What should be here?
}

hard

A. current.next = head; return head;

B. current.next = null; return head;

C. head.next = current; return current;

D. return current;

Solution

1. Step 1: Create nodes from array and link linearly

   Loop creates nodes for each array element and links them in order.

2. Step 2: Make the list circular by linking last node to head

   Setting current.next = head closes the loop, making the list circular.

3. Step 3: Return the head node

   Return head to provide access to the circular list.

4. Final Answer:

   current.next = head; return head; -> Option A

5. Quick Check:

   Last node points to head to form circle [OK]

Hint: Close circle by linking last node to head [OK]

Common Mistakes:

• Leaving last node next as null
• Returning last node instead of head
• Linking head.next to last node instead of last.next to head