Delete Node at End in DSA C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Delete Node at End' mean in a linked list?

It means removing the last node from a linked list, so the list ends one node earlier.

beginner

In a singly linked list, why do we need to traverse the list to delete the last node?

Because we only have a pointer to the head and each node points forward, we must find the second last node to update its next pointer to null.

beginner

What happens if you delete the last node in a linked list with only one node?

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

intermediate

Show the key steps to delete the last node in a singly linked list.

1. Check if list is empty (head is nullptr). 2. If only one node, set head to nullptr. 3. Otherwise, traverse to second last node. 4. Set second last node's next to nullptr. 5. Delete last node.

intermediate

Why can't we delete the last node directly in a singly linked list without traversal?

Because nodes only know their next node, not the previous one, so we can't update the previous node's next pointer without finding it first.

What is the first step when deleting the last node in a singly linked list?

A Check if the list is empty

B Traverse to the last node

C Set head to null

D Delete the head node

Always check if the list is empty to avoid errors.

If a singly linked list has only one node, what should happen when deleting the last node?

A Do nothing

B Set last node's next to null

C Traverse to second last node

D Set head to null

Deleting the only node empties the list, so head must be null.

Why do we traverse to the second last node before deleting the last node?

A To delete it instead

B To find the head

C To update its next pointer to null

D To reverse the list

We update the second last node's next pointer to null to remove the last node.

What happens if you try to delete the last node without updating the previous node's next pointer?

A The list will have a dangling pointer

B The list becomes empty

C The head changes

D Nothing happens

The previous node still points to deleted memory, causing errors.

In a singly linked list, can you delete the last node in O(1) time without extra pointers?

A Yes, always

B No, you must traverse the list

C Only if the list is empty

D Only if the list has one node

Without a pointer to the previous node, traversal is needed.

Explain how to delete the last node in a singly linked list step-by-step.

Think about what happens if the list has zero, one, or many nodes.

Why is traversal necessary to delete the last node in a singly linked list?

Consider how nodes are connected in a singly linked list.

Practice

1. What happens when you delete the last node in a singly linked list?

easy

A. The second last node's next pointer becomes null

B. The head pointer is set to null

C. The first node is deleted instead

D. All nodes are deleted

Solution

1. Step 1: Understand the linked list structure

   Each node points to the next node. The last node points to null.

2. Step 2: Effect of deleting the last node

   Deleting the last node means the previous node's next pointer must be set to null to mark new end.

3. Final Answer:

   The second last node's next pointer becomes null -> Option A

4. Quick Check:

   Last node removed, previous node points to null [OK]

Hint: Last node removal sets previous node's next to null [OK]

Common Mistakes:

• Setting head to null incorrectly
• Deleting the first node instead
• Not updating the previous node's next pointer

2. Which of the following is the correct syntax to delete the last node in a singly linked list in C++?

easy

A. delete lastNode->prev; lastNode->prev = nullptr;

B. delete lastNode; lastNode = nullptr;

C. delete head; head = nullptr;

D. delete lastNode->next; lastNode->next = nullptr;

Solution

1. Step 1: Identify the last node's pointer

   In singly linked list, last node's previous node points to it via next pointer.

2. Step 2: Delete last node and update pointer

   Deleting lastNode->next and setting lastNode->next to nullptr correctly removes last node.

3. Final Answer:

   delete lastNode->next; lastNode->next = nullptr; -> Option D

4. Quick Check:

   Delete next node and set pointer null [OK]

Hint: Delete node via previous node's next pointer [OK]

Common Mistakes:

• Deleting head instead of last node
• Using prev pointer in singly linked list
• Not setting pointer to nullptr after delete

3. What will be the output linked list after deleting the last node from the list: 10 -> 20 -> 30 -> 40 -> null?

medium

A. 10 -> 20 -> null

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

C. 20 -> 30 -> 40 -> null

D. 10 -> 20 -> 30 -> 40 -> null

Solution

1. Step 1: Identify the last node

   The last node is 40, which points to null.

2. Step 2: Remove last node and update previous node

   Deleting 40 means 30's next pointer becomes null, ending list at 30.

3. Final Answer:

   10 -> 20 -> 30 -> null -> Option B

4. Quick Check:

   Last node 40 removed, list ends at 30 [OK]

Hint: Last node removed, previous node points to null [OK]

Common Mistakes:

• Not updating previous node's next pointer
• Deleting head node by mistake
• Outputting original list without deletion

4. Given the code snippet below, what is the error when deleting the last node?

struct Node {
  int data;
  Node* next;
};

void deleteLast(Node*& head) {
  if (head == nullptr) return;
  Node* temp = head;
  while (temp->next != nullptr) {
    temp = temp->next;
  }
  delete temp;
  temp = nullptr;
}

medium

A. Uses wrong pointer type for deletion

B. Deletes head node instead of last node

C. Does not update previous node's next pointer to null

D. No error, code works correctly

Solution

1. Step 1: Analyze traversal to last node

   The loop moves temp to last node, but does not track previous node.

2. Step 2: Identify missing pointer update

   Deleting temp frees last node but previous node's next still points to freed memory, causing dangling pointer.

3. Final Answer:

   Does not update previous node's next pointer to null -> Option C

4. Quick Check:

   Previous node's next must be null after deletion [OK]

Hint: Track previous node to update next pointer before delete [OK]

Common Mistakes:

• Not tracking previous node in traversal
• Deleting node without updating links
• Setting temp to nullptr does not fix list

5. You have a singly linked list with only one node. What should happen when you delete the last node?

hard

A. Set head pointer to null

B. Set node's next pointer to null

C. Delete node but keep head pointing to it

D. Do nothing, list remains same

Solution

1. Step 1: Identify single node list condition

   Only one node means head points to that node and node's next is null.

2. Step 2: Delete node and update head

   Deleting the only node requires setting head to null to mark empty list.

3. Final Answer:

   Set head pointer to null -> Option A

4. Quick Check:

   Single node deleted means empty list head = null [OK]

Hint: Single node deletion empties list, head = null [OK]

Common Mistakes:

• Not setting head to null after deletion
• Trying to update next pointer of deleted node
• Leaving dangling pointer in head