Delete a Node from Circular Linked List in DSA Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a circular linked list?

A circular linked list is a linked list where the last node points back to the first node, forming a circle with no null end.

intermediate

Why is deleting a node from a circular linked list different from a singly linked list?

Because the last node points back to the head, we must update the last node's next pointer if the head or any node is deleted to maintain the circle.

intermediate

What steps are involved in deleting the head node in a circular linked list?

1. Find the last node (which points to head). 2. Update last node's next to head's next. 3. Update head to head's next. 4. Remove old head.

beginner

What happens if you delete the only node in a circular linked list?

The list becomes empty, so the head pointer should be set to null.

beginner

In Java, how do you check if a circular linked list is empty?

Check if the head pointer is null. If it is null, the list is empty.

In a circular linked list, what does the last node point to?

A Itself

B Null

C The first node

D The previous node

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

When deleting the head node in a circular linked list, what must you update?

A The last node's next pointer

B Only the head pointer

C The previous node's next pointer

D Nothing

The last node's next pointer must be updated to point to the new head to maintain the circular structure.

What should you do if you delete the only node in a circular linked list?

A Set head to itself

B Do nothing

C Set last node's next to null

D Set head to null

If the only node is deleted, the list becomes empty, so head should be set to null.

Which of these is NOT a step when deleting a node from a circular linked list?

A Set the node's value to null without changing pointers

B Update the previous node's next pointer

C Update the last node's next pointer if needed

D Find the node to delete

Simply setting the node's value to null does not remove it from the list; pointers must be updated.

How do you identify the last node in a circular linked list?

A It has the highest value

B Its next pointer points to the head

C It has no next node

D Its next pointer is null

The last node's next pointer points back to the head node in a circular linked list.

Explain the process of deleting a node from a circular linked list, including special cases.

Think about how the circle is maintained after deletion.

Describe how to delete the head node in a circular linked list and why it is different from deleting other nodes.

Focus on the special role of the head and last nodes.

Practice

1. What happens when you delete the only node in a circular linked list?

easy

A. The list becomes empty (head points to null)

B. The list still contains the deleted node

C. The list forms a linear linked list

D. The list throws an error automatically

Solution

1. Step 1: Understand single node deletion

   When the only node is deleted, no nodes remain in the list.

2. Step 2: Resulting list state

   The head pointer is set to null, indicating an empty list.

3. Final Answer:

   The list becomes empty (head points to null) -> Option A

4. Quick Check:

   Deleting last node empties list [OK]

Hint: Deleting last node empties list, head = null [OK]

Common Mistakes:

• Assuming list still has nodes after deletion
• Not setting head to null
• Confusing circular with linear list after deletion

2. Which of the following is the correct way to update the head when deleting the head node in a circular linked list?

easy

A. head = tail; tail.next = null;

B. head = null; tail = null;

C. head = head.prev; tail.next = head;

D. head = head.next; tail.next = head;

Solution

1. Step 1: Update head pointer

   When deleting the head node, move head to next node.

2. Step 2: Maintain circular link

   Update tail's next pointer to new head to keep circular structure.

3. Final Answer:

   head = head.next; tail.next = head; -> Option D

4. Quick Check:

   Head moves forward, tail links to new head [OK]

Hint: After deleting head, point tail.next to new head [OK]

Common Mistakes:

• Setting tail.next to null breaks circular link
• Setting head to null incorrectly
• Using head.prev which doesn't exist in singly circular list

3. What will be the output after deleting node with value 3 from this circular linked list: 1 -> 2 -> 3 -> 4 -> (back to 1)?

Node head = new Node(1);
Node n2 = new Node(2);
Node n3 = new Node(3);
Node n4 = new Node(4);
head.next = n2; n2.next = n3; n3.next = n4; n4.next = head;
// Delete node with value 3
// After deletion, print list starting from head

medium

A. 1 -> 2 -> 4 -> (back to 1)

B. 1 -> 2 -> 3 -> 4 -> (back to 1)

C. 1 -> 4 -> (back to 1)

D. 2 -> 4 -> (back to 2)

Solution

1. Step 1: Locate node with value 3

   Traverse list: 1 -> 2 -> 3 found.

2. Step 2: Remove node 3 by linking 2 to 4

   Set n2.next = n3.next (which is n4), skipping node 3.

3. Final Answer:

   1 -> 2 -> 4 -> (back to 1) -> Option A

4. Quick Check:

   Node 3 removed, list links 2 to 4 [OK]

Hint: Skip node by linking previous to next [OK]

Common Mistakes:

• Not updating previous node's next pointer
• Breaking circular link by missing tail update
• Deleting wrong node or skipping nodes

4. Identify the error in this code snippet that deletes a node with value 'key' from a circular linked list:

Node current = head;
while(current.next != head && current.next.data != key) {
    current = current.next;
}
if(current.next.data == key) {
    current.next = current.next.next;
}

medium

A. Does not handle deletion when list has only one node

B. Infinite loop if key not found

C. Does not update tail pointer when deleting last node

D. Deletes head node incorrectly

Solution

1. Step 1: Check tail update on deletion

   If deleted node is tail, tail pointer must update to current node.

2. Step 2: Code misses tail update

   Code only changes current.next, tail remains pointing to deleted node.

3. Final Answer:

   Does not update tail pointer when deleting last node -> Option C

4. Quick Check:

   Tail pointer must update if last node deleted [OK]

Hint: Update tail if deleting last node [OK]

Common Mistakes:

• Ignoring tail pointer update
• Assuming tail auto-updates
• Not checking if deleted node is tail

5. Given a circular linked list with nodes 10 -> 20 -> 30 -> 40 -> (back to 10), how would you delete the node with value 10 (head node) and maintain the circular structure? Choose the correct sequence of operations.

hard

A. Set head = null; tail = null;

B. Set head = head.next; tail.next = head; delete old head;

C. Set tail.next = head.next; head = head.next;

D. Set tail = head; head = head.next; tail.next = null;

Solution

1. Step 1: Move head to next node

   Set head = head.next to remove old head from start.

2. Step 2: Update tail's next pointer

   Set tail.next = head to maintain circular link.

3. Step 3: Delete old head node properly

   Remove old head node from memory if needed.

4. Final Answer:

   Set head = head.next; tail.next = head; delete old head; -> Option B

5. Quick Check:

   Head moves forward, tail links to new head [OK]

Hint: Update head and tail.next to new head when deleting head [OK]

Common Mistakes:

• Breaking circular link by setting tail.next to null
• Not moving head pointer
• Deleting head without updating tail.next