Delete a Node from Circular Linked List in DSA Python - Execution Trace

Concept Flow - Delete a Node from Circular Linked List

Start at head

↓

Check if list empty?

Yes→Stop: Nothing to delete

No↓

Traverse nodes to find target

↓

Found node to delete?

No→Stop: Node not found

Yes↓

If node is head

↓

Adjust head and last node's next

↓

Else

↓

Adjust previous node's next

↓

Delete node

↓

Done

Start from head, check if list is empty, traverse to find node, adjust pointers depending on node position, then delete node.

Execution Sample

DSA Python

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

def delete_node(head, key):
    # Deletes node with value key from circular linked list
    pass

Deletes a node with given value from a circular linked list, adjusting pointers to maintain circularity.

Execution Table

Step	Operation	Nodes in List	Pointer Changes	Visual State
1	Start at head	1 -> 2 -> 3 -> 4 -> (back to 1)	head points to node 1	1 -> 2 -> 3 -> 4 -> (head)
2	Check if list empty	1 -> 2 -> 3 -> 4 -> (back to 1)	No change	1 -> 2 -> 3 -> 4 -> (head)
3	Traverse to find node with data=3	1 -> 2 -> 3 -> 4 -> (back to 1)	current moves: 1->2->3	1 -> 2 -> [3] -> 4 -> (head)
4	Found node to delete (3)	1 -> 2 -> 3 -> 4 -> (back to 1)	prev.next updated from 3 to 4	1 -> 2 -> 4 -> (head)
5	Delete node 3	1 -> 2 -> 4 -> (back to 1)	Node 3 removed	1 -> 2 -> 4 -> (head)
6	End	1 -> 2 -> 4 -> (back to 1)	No change	1 -> 2 -> 4 -> (head)

💡 Node with data=3 deleted, pointers adjusted to maintain circular list

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
head	Node 1	Node 1	Node 1	Node 1
current	Node 1	Node 3	Node 3	Node 1
prev	None	Node 2	Node 2	Node 2
list size	4	4	3	3

Key Moments - 3 Insights

Why do we need to track the previous node (prev) when deleting?

Because in a singly linked circular list, to remove the current node, we must update the previous node's next pointer to skip the deleted node. See execution_table step 4 where prev.next changes.

What happens if the node to delete is the head?

We must update the head pointer and also the last node's next pointer to the new head to keep the list circular. This is a special case not shown in this example but important to handle.

Why does traversal stop when current.data == key?

Because we found the node to delete. Continuing would risk infinite loop in circular list. See execution_table step 3 and 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'current' after step 3?

A Node 2

B Node 4

C Node 3

D Node 1

💡 Hint

Check the 'current' variable in variable_tracker after step 3.

At which step is the node with data=3 removed from the list?

A Step 5

B Step 3

C Step 4

D Step 6

💡 Hint

Look at the 'Operation' and 'Visual State' columns in execution_table.

If the node to delete was the head, what pointer must be updated besides 'prev.next'?

A Only the head pointer

B The head pointer and last node's next pointer

C Only the last node's next pointer

D No pointers need updating

💡 Hint

Refer to key_moments about deleting the head node.

Concept Snapshot

Delete Node in Circular Linked List:
- Start at head, check if list empty
- Traverse to find node with target data
- Keep track of previous node
- If node found:
  - If head, update head and last node's next
  - Else, update prev.next to skip node
- Delete node and maintain circular link

Full Transcript

To delete a node from a circular linked list, start at the head and check if the list is empty. If not, traverse the list to find the node with the target value, keeping track of the previous node. When found, if the node is the head, update the head pointer and the last node's next pointer to maintain circularity. Otherwise, update the previous node's next pointer to skip the node to be deleted. Finally, remove the node and ensure the list remains circular.