Insert at Beginning of Circular Linked List in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Java

Node newNode = new Node([1]);

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

Anext

Bhead

Cnull

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'head' instead of 'data' when creating the new node.

Passing 'null' or 'next' which are not the data values.

We create a new node by passing the data value to the Node constructor.

2fill in blank

medium

Complete the code to check if the list is empty.

DSA Java

if ([1] == null) {

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

Ahead

BnewNode

Ctail

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Checking newNode instead of head.

Checking tail or next which may not be null even if list is empty.

The list is empty if the head pointer is null.

3fill in blank

hard

Fix the error in updating the tail's next pointer to the new node.

DSA Java

tail.[1] = newNode;

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

Ahead

Bprev

Cnext

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using tail.prev which does not exist in singly circular list.

Assigning to tail.data or tail.head which are incorrect.

In a circular linked list, tail's next pointer should point to the new node.

4fill in blank

hard

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

DSA Java

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

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

Anext

BnewNode

Chead

Dtail

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of assignment.

Setting head to old head instead of newNode.

The new node's next points to the old head, then head is updated to newNode.

5fill in blank

hard

Fill all three blanks to complete the insert at beginning method for circular linked list.

DSA Java

public void insertAtBeginning(int data) {
    Node newNode = new Node([1]);
    if (head == null) {
        head = newNode;
        tail = newNode;
        newNode.[2] = head;
    } else {
        newNode.next = head;
        tail.[3] = newNode;
        head = newNode;
    }
}

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

Adata

Bnext

Dprev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' instead of 'next' for pointers.

Not updating tail.next in else block.

Not setting newNode.next to head when list is empty.

Create new node with data; if empty, point newNode.next to head; else update tail.next to newNode.

Practice

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

easy

A. The new node becomes the head and points to the old head, maintaining the circular link.

B. The new node is added at the end of the list, breaking the circular link.

C. The new node replaces the last node in the list.

D. The list becomes linear and loses its circular property.

Solution

1. Step 1: Understand the circular linked list structure

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

2. Step 2: Insert new node at beginning

   The new node is linked to the current head, and the last node's next pointer is updated to this new node, making it the new head.

3. Final Answer:

   The new node becomes the head and points to the old head, maintaining the circular link. -> Option A

4. Quick Check:

   New head points to old head, circle intact = C [OK]

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

Common Mistakes:

• Forgetting to update last node's next pointer
• Breaking the circular link by not linking last node
• Replacing last node instead of adding new head

2. Which of the following Java code snippets correctly inserts a new node at the beginning of a circular linked list?

easy

A. last.next = head; head = newNode; newNode.next = last;

B. head.next = newNode; newNode.next = last; last = newNode;

C. newNode.next = null; head = newNode; last.next = head;

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

Solution

1. Step 1: Link new node to current head

   Set newNode.next = head to point new node to the current head.

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

   Set last.next = newNode to maintain circular link, then update head = newNode.

3. Final Answer:

   newNode.next = head; last.next = newNode; head = newNode; -> Option D

4. Quick Check:

   Correct pointer updates = A [OK]

Hint: Link new node to head, update last.next, then move head [OK]

Common Mistakes:

• Setting newNode.next to null breaks circular link
• Not updating last.next to new node
• Incorrect order of pointer updates

3. What will be the output of the following code snippet after inserting a node with value 10 at the beginning of the circular linked list?

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

Node head = new Node(20);
Node second = new Node(30);
head.next = second;
second.next = head; // circular link

Node newNode = new Node(10);
// Insert at beginning
newNode.next = head;
second.next = newNode;
head = newNode;

// Print list starting from head
Node temp = head;
do {
  System.out.print(temp.data + " -> ");
  temp = temp.next;
} while(temp != head);
System.out.print("null");

medium

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

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

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

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

Solution

1. Step 1: Understand initial list and insertion

   Initial list: 20 -> 30 -> back to 20. New node 10 inserted at beginning, so head moves to 10.

2. Step 2: Trace the print loop

   Starting at head (10), print 10, then 20, then 30, then loop ends at head again.

3. Final Answer:

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

4. Quick Check:

   New head 10 followed by old nodes = D [OK]

Hint: Start printing from new head, follow next pointers until back to head [OK]

Common Mistakes:

• Printing nodes in wrong order
• Not updating last node's next pointer
• Confusing circular link with null termination

4. Identify the error in the following code that attempts to insert a new node at the beginning of a circular linked list:

Node newNode = new Node(5);
newNode.next = head;
head = newNode;
// Missing update of last node's next pointer

medium

A. The head should not be updated before updating last node's next pointer.

B. The new node's next pointer should be null instead of head.

C. The last node's next pointer is not updated to point to the new head, breaking the circular link.

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

Solution

1. Step 1: Check pointer updates after insertion

   New node points to old head, and head is updated, but last node still points to old head.

2. Step 2: Identify circular link break

   Since last node's next is not updated to new head, the circular link breaks, causing incorrect list traversal.

3. Final Answer:

   The last node's next pointer is not updated to point to the new head, breaking the circular link. -> Option C

4. Quick Check:

   Last node must point to new head to keep circle [OK]

Hint: Always update last.next to new head after insertion [OK]

Common Mistakes:

• Forgetting to update last node's next pointer
• Assuming head update is enough
• Not maintaining circular property

5. Given a circular linked list with nodes 5 -> 15 -> 25 -> back to 5, write the sequence of node values after inserting a new node with value 1 at the beginning. Assume the insertion updates all pointers correctly. What is the resulting list?

hard

A. 5 -> 15 -> 25 -> 1 -> null

B. 1 -> 5 -> 15 -> 25 -> null

C. 1 -> 15 -> 25 -> 5 -> null

D. 25 -> 5 -> 15 -> 1 -> null

Solution

1. Step 1: Insert new node at beginning

   New node with value 1 points to old head (5), and last node (25) points to new node.

2. Step 2: Update head pointer

   Head is updated to new node (1), so traversal starts from 1.

3. Final Answer:

   1 -> 5 -> 15 -> 25 -> null -> Option B

4. Quick Check:

   New head 1 followed by old nodes in order [OK]

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

Common Mistakes:

• Not updating last node's next pointer
• Incorrect order of nodes after insertion
• Confusing circular list with linear list