Delete a Node from Circular Linked List in DSA Go - 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 is deleted to keep the circle intact.

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 (or nil in Go).

beginner

In Go, how do you represent a node in a circular linked list?

type Node struct { data int; next *Node } where next points to the next node, and the last node's next points back to the head.

intermediate

What is the key step to delete a node with a given value in a circular linked list?

Find the node before the target node, update its next pointer to skip the target node, and if the target is head, update head accordingly.

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

A Itself

B Null

C The first node

D The middle node

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

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

A Update the last node's next pointer to the new head

B Do nothing

C Set head to null immediately

D Delete the entire list

When deleting the head, the last node's next pointer must point to the new head to maintain the circle.

If the circular linked list has only one node and you delete it, what is the new state of the list?

A List remains unchanged

B Empty list (head is null)

C List with two nodes

D List with one node pointing to itself

Deleting the only node leaves the list empty, so head should be set to null.

Which pointer do you update to remove a node from a circular linked list?

A The last node's previous pointer

B The node's own next pointer

C The head pointer only

D The previous node's next pointer

You update the previous node's next pointer to skip the node to be deleted.

What is the time complexity to delete a node by value in a circular linked list?

A O(n)

B O(1)

C O(log n)

D O(n^2)

You may need to traverse the list to find the node, so deletion by value is O(n).

Explain step-by-step how to delete a node with a given value from a circular linked list.

Think about how the circle is maintained after deletion.

Describe how the circular linked list structure changes when deleting the head node.

Focus on pointers that keep the circle intact.

Practice

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

easy

A. The list still contains the deleted node.

B. The list becomes empty (head points to nil).

C. The list forms a linear linked list.

D. The list throws an error automatically.

Solution

1. Step 1: Understand single-node circular list

   A circular linked list with one node points to itself.

2. Step 2: Delete the only node

   Removing this node means no nodes remain, so head becomes nil.

3. Final Answer:

   The list becomes empty (head points to nil). -> Option B

4. Quick Check:

   Single node deleted = empty list [OK]

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

Common Mistakes:

• Assuming list still has nodes after deleting the only node
• Not updating head to nil
• Confusing circular with linear list after deletion

2. Which Go syntax correctly moves the head pointer when deleting the head node from a circular linked list?

easy

A. head.next = head

B. head = nil.next

C. head = head.next

D. head = head.prev

Solution

1. Step 1: Identify head deletion logic

   Deleting head means moving head pointer to next node.

2. Step 2: Check syntax correctness

   Assigning head = head.next correctly moves head to next node.

3. Final Answer:

   head = head.next -> Option C

4. Quick Check:

   Move head to next node = head = head.next [OK]

Hint: Move head pointer to next node to delete head [OK]

Common Mistakes:

• Using nil.next causes runtime error
• Assigning head.next = head does not delete node
• Using head.prev is invalid for singly circular list

3. Given this circular linked list: 1 -> 2 -> 3 -> (back to 1), what is the list after deleting node with value 2?

medium

A. 1 -> 3 -> (back to 1)

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

C. 2 -> 3 -> (back to 2)

D. 3 -> 1 -> (back to 3)

Solution

1. Step 1: Locate node with value 2

   Node 2 is between nodes 1 and 3 in the circular list.

2. Step 2: Remove node 2 by linking 1 to 3

   Update node 1's next pointer to node 3, skipping node 2.

3. Final Answer:

   1 -> 3 -> (back to 1) -> Option A

4. Quick Check:

   Deleted 2, linked 1 to 3 [OK]

Hint: Link previous node to next of deleted node [OK]

Common Mistakes:

• Not updating previous node's next pointer
• Deleting wrong node
• Breaking circular link

4. What is wrong with this Go code snippet for deleting a node from a circular linked list?

func deleteNode(head *Node, key int) *Node {
  if head == nil {
    return nil
  }
  curr := head
  for curr.next != head && curr.next.data != key {
    curr = curr.next
  }
  if curr.next.data == key {
    curr.next = curr.next.next
  }
  return head
}

medium

A. It returns nil always.

B. It causes infinite loop always.

C. It deletes all nodes with the key.

D. It does not handle deleting the head node correctly.

Solution

1. Step 1: Analyze deletion logic

   The code searches for node before target and skips target node.

2. Step 2: Check head deletion case

   If the node to delete is head, head pointer is not updated, causing incorrect list.

3. Final Answer:

   It does not handle deleting the head node correctly. -> Option D

4. Quick Check:

   Head deletion needs head pointer update [OK]

Hint: Update head if deleting head node [OK]

Common Mistakes:

• Ignoring head node deletion
• Not updating head pointer
• Assuming key always exists

5. You have a circular linked list: 10 -> 20 -> 30 -> 40 -> (back to 10). You want to delete node with value 10 (head). Which steps correctly update the list?

hard

A. Find last node (40), set its next to head.next (20), then update head to 20.

B. Set head to nil directly without updating last node.

C. Delete node 10 by setting head.next to nil.

D. Swap data of head and next node, then delete next node.

Solution

1. Step 1: Find last node pointing to head

   Traverse list to find node 40 which points to head (10).

2. Step 2: Update last node's next pointer

   Set node 40's next to head.next (node 20) to maintain circularity.

3. Step 3: Update head pointer

   Set head to head.next (node 20) to delete original head.

4. Final Answer:

   Find last node (40), set its next to head.next (20), then update head to 20. -> Option A

5. Quick Check:

   Update last node and head to delete head node [OK]

Hint: Update last node's next and head to delete head [OK]

Common Mistakes:

• Not updating last node's next pointer
• Setting head to nil breaks list
• Deleting node by setting next to nil