Delete a Node from Circular Linked List in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to move the pointer to the next node in the circular linked list.

DSA C++

current = current[1];

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

A->prev

B.prev

C.next

D->next

Attempts:

3 left

💡 Hint

Common Mistakes

Using '.next' instead of '->next' causes syntax errors.

Using 'prev' moves backward, not forward.

In a circular linked list, to move to the next node, we use the pointer ->next.

2fill in blank

medium

Complete the condition to check if the list has only one node.

DSA C++

if (head != nullptr && head[1] == head) {

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

A.prev

B->prev

C->next

D.next

Attempts:

3 left

💡 Hint

Common Mistakes

Using '.next' instead of '->next' causes errors.

Checking 'prev' pointer instead of 'next'.

In a circular linked list, if the head's next pointer points to itself, it means there is only one node.

3fill in blank

hard

Fix the error in the loop condition to find the node before the one to delete.

DSA C++

while (current->next != head && current->next->data != key) {
    current = current[1];
}

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

A->next

B.next

C->prev

D.prev

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' moves backward, causing infinite loops.

Using '.' instead of '->' causes syntax errors.

To traverse forward in the circular linked list, use current = current->next;.

4fill in blank

hard

Fill both blanks to correctly update pointers when deleting a node in the circular linked list.

DSA C++

current->next = current->next[1];
current->next[2] = current;

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

A->next

B->prev

C.next

D.prev

Attempts:

3 left

💡 Hint

Common Mistakes

Using '.' instead of '->' causes errors.

Mixing up next and prev pointers.

To delete a node, link current's next to the node after the deleted node, and update the previous pointer of that node to current.

5fill in blank

hard

Fill all three blanks to correctly handle deleting the head node in a circular linked list.

DSA C++

if (head->data == key) {
    Node* temp = head;
    while (temp->next != head) {
        temp = temp[1];
    }
    temp->next = head[2];
    head[2]->prev = temp;
    head = head[3];
}

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

A->prev

B->next

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' to find last node causes infinite loop.

Not updating head pointer after deletion.

To delete the head, find the last node by moving forward with '->next', then link it to the new head which is head's next node.

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 one node pointing to itself.

C. The list becomes a linear linked list.

D. The list throws an error and stops.

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 leaves no nodes, so head becomes null.

3. Final Answer:

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

4. Quick Check:

   Single node deleted = empty list [OK]

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

Common Mistakes:

• Assuming list still has one node after deletion
• Not updating head to null
• Confusing circular with linear list after deletion

2. Which of the following is the correct syntax to delete a node with value key from a circular linked list in C++?

easy

A. void deleteNode(Node head, int key) { /* code */ }

B. void deleteNode(Node* head, int key) { /* code */ }

C. void deleteNode(Node*& head, int key) { /* code */ }

D. void deleteNode(int key, Node* head) { /* code */ }

Solution

1. Step 1: Understand pointer passing in C++

   To modify the head pointer itself, pass it by reference (Node*& head).

2. Step 2: Check parameter order and types

   Function should accept head reference first, then key to delete.

3. Final Answer:

   void deleteNode(Node*& head, int key) { /* code */ } -> Option C

4. Quick Check:

   Pass head by reference to modify it [OK]

Hint: Pass head as reference to update list head [OK]

Common Mistakes:

• Passing head by value (won't update original list)
• Wrong parameter order
• Passing head as object, not pointer or reference

3. Given the circular linked list: 10 -> 20 -> 30 -> (back to 10), what is the list after deleting node with value 20?

medium

A. 10 -> 20 -> 30 -> (back to 10)

B. 10 -> 30 -> (back to 10)

C. 20 -> 30 -> (back to 20)

D. 30 -> 10 -> (back to 30)

Solution

1. Step 1: Identify node to delete

   Node with value 20 is between 10 and 30.

2. Step 2: Remove node 20 and link 10 to 30

   Update 10's next pointer to 30, maintaining circular link.

3. Final Answer:

   10 -> 30 -> (back to 10) -> Option B

4. Quick Check:

   Deleted 20, linked 10 to 30 [OK]

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

Common Mistakes:

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

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

void deleteNode(Node*& head, int key) {
  if (!head) return;
  Node* curr = head;
  while (curr->next != head && curr->next->data != key) {
    curr = curr->next;
  }
  if (curr->next->data == key) {
    Node* temp = curr->next;
    curr->next = temp->next;
    delete temp;
  }
}

medium

A. Does not handle deleting the head node correctly.

B. Does not check if list is empty.

C. Deletes node without updating pointers.

D. Infinite loop due to wrong while condition.

Solution

1. Step 1: Analyze deletion logic

   Code searches for node before target and deletes next node.

2. Step 2: Check head deletion case

   If node to delete is head, head pointer is not updated, causing errors.

3. Final Answer:

   Does not handle deleting the head node correctly. -> Option A

4. Quick Check:

   Head deletion needs special handling [OK]

Hint: Update head if deleted node is head [OK]

Common Mistakes:

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

5. You have a circular linked list: 5 -> 15 -> 25 -> 35 -> (back to 5). You want to delete the node with value 5 (head node). Which steps correctly update the list?

hard

A. Swap head data with next node and delete next node.

B. Delete head node directly without updating last node's next.

C. Set head to null without deleting any node.

D. Find last node (35), set its next to head's next (15), update head to 15.

Solution

1. Step 1: Locate last node

   Traverse list to find node pointing to head (value 35).

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

   Set last node's next to head's next (node with value 15).

3. Step 3: Update head pointer

   Set head to head's next (15) to maintain circular list.

4. Final Answer:

   Find last node (35), set its next to head's next (15), update head to 15. -> Option D

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
• Not updating head pointer
• Deleting head without fixing links