Delete Node at End in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to move to the last node in a singly linked list.

DSA Python

while current.next [1] None:
    current = current.next

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

A==

B!=

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '!=' causes the loop to stop immediately.

Using '<' or '>' is invalid for None comparison.

The loop continues while current.next is not None, meaning current is not the last node.

2fill in blank

medium

Complete the code to update the second last node's next pointer to None, deleting the last node.

DSA Python

prev.next [1] None

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

A->

B==

C=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '=' causes a comparison, not assignment.

Using '!=' or '->' are syntax errors here.

We assign None to prev.next to remove the last node from the list.

3fill in blank

hard

Fix the error in the loop condition to find the second last node.

DSA Python

while current.next.next [1] None:
    current = current.next

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

A!=

B>

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' causes the loop to stop too early.

Using '<' or '>' is invalid for None comparison.

The loop continues while current.next.next is not None, so current stops at second last node.

4fill in blank

hard

Fill both blanks to correctly handle deleting the last node when list has only one node.

DSA Python

if head.next [1] None:
    head [2] None

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

A==

B!=

C=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' in the if condition causes wrong logic.

Using '==' instead of '=' for assignment causes errors.

If head.next is None, it means only one node exists, so set head to None to delete it.

5fill in blank

hard

Fill all three blanks to complete the function that deletes the last node of a singly linked list.

DSA Python

def delete_last_node(head):
    if head is None:
        return None
    if head.next [1] None:
        return [2]
    current = head
    while current.next.next [3] None:
        current = current.next
    current.next = None
    return head

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

A==

Bhead

C!=

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' in the if condition causes wrong logic.

Returning head instead of None for single node case.

Using '==' instead of '!=' in the loop condition causes the loop to stop too early.

If head.next == None, list has one node, so return None after deleting it. Loop while current.next.next != None to reach second last node.

Practice

1. What is the main purpose of the Delete Node at End operation in a singly linked list?

easy

A. Remove the first node from the linked list

B. Add a new node at the end of the linked list

C. Remove the last node from the linked list

D. Reverse the linked list

Solution

1. Step 1: Understand the operation

   The operation aims to remove a node from the end of the singly linked list.

2. Step 2: Identify the correct description

   Removing the last node means deleting the tail node, not adding or reversing nodes.

3. Final Answer:

   Remove the last node from the linked list -> Option C

4. Quick Check:

   Delete Node at End = Remove last node [OK]

Hint: Deleting at end means removing the last node [OK]

Common Mistakes:

• Confusing delete at end with delete at beginning
• Thinking it adds a node instead of removing
• Mixing up with reversing the list

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

easy

A. Set last node's next to head

B. Set head = null directly

C. Create a new node and assign it to head

D. Traverse to second last node and set its next to null

Solution

1. Step 1: Understand deletion at end

   To delete the last node, we must find the second last node and make its next pointer null.

2. Step 2: Check each option

   Setting head = null deletes the whole list, not just last node. Setting last node's next to head creates a cycle. Creating a new node and assigning to head adds a node, not deletes.

3. Final Answer:

   Traverse to second last node and set its next to null -> Option D

4. Quick Check:

   Delete last node = second last node next = null [OK]

Hint: Set second last node's next to null to delete last node [OK]

Common Mistakes:

• Setting head to null deletes entire list
• Creating cycles by wrong pointer assignments
• Adding nodes instead of deleting

3. What will be the output linked list after deleting the last node from the list: 1 -> 2 -> 3 -> 4 -> null?

medium

A. 1 -> 2 -> 3 -> null

B. 1 -> 2 -> 3 -> 4 -> null

C. 2 -> 3 -> 4 -> null

D. 1 -> 2 -> null

Solution

1. Step 1: Identify the last node

   The last node in the list is the node with value 4.

2. Step 2: Delete the last node

   Removing node 4 means the new last node is 3, so the list ends at 3 with next as null.

3. Final Answer:

   1 -> 2 -> 3 -> null -> Option A

4. Quick Check:

   Last node 4 removed = 1 -> 2 -> 3 [OK]

Hint: Last node removed means list ends one node earlier [OK]

Common Mistakes:

• Not updating second last node's next to null
• Removing wrong node (like first node)
• Confusing output with original list

4. Consider this code snippet to delete the last node of a singly linked list:

def delete_end(head):
    if head is None:
        return None
    if head.next is None:
        return None
    temp = head
    while temp.next is not None:
        temp = temp.next
    temp.next = None
    return head

What is the error in this code?

medium

A. The loop never stops because condition is wrong

B. temp.next is null check misses second last node

C. It deletes the first node instead of last

D. No error, code works correctly

Solution

1. Step 1: Analyze the loop condition

   The loop runs while temp.next is not null, so temp moves to the last node.

2. Step 2: Identify pointer update mistake

   After loop, temp points to last node, but to delete last node, we need second last node to set its next to null. Here, temp.next = null sets last node's next to null, which is already null, so no deletion happens.

3. Final Answer:

   temp.next is null check misses second last node -> Option B

4. Quick Check:

   Must stop at second last node to delete last [OK]

Hint: Stop at second last node, not last, to delete end node [OK]

Common Mistakes:

• Stopping loop at last node instead of second last
• Not handling single node list correctly
• Setting wrong pointers causing no deletion

5. Given a singly linked list with nodes 10 -> 20 -> 30 -> 40 -> 50 -> null, write the steps to delete the last node and then add a new node with value 60 at the end. What will be the final list?

hard

A. 10 -> 20 -> 30 -> 40 -> 60 -> null

B. 10 -> 20 -> 30 -> 40 -> 50 -> 60 -> null

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

D. 10 -> 20 -> 30 -> 40 -> 50 -> null

Solution

1. Step 1: Delete the last node (50)

   Traverse to second last node (40) and set its next to null, removing 50.

2. Step 2: Add new node with value 60 at end

   Traverse to last node (40) and set its next to new node with value 60, new node's next is null.

3. Final Answer:

   10 -> 20 -> 30 -> 40 -> 60 -> null -> Option A

4. Quick Check:

   Delete last 50, add 60 at end = 10->20->30->40->60 [OK]

Hint: Delete last node, then link new node at end [OK]

Common Mistakes:

• Not updating second last node's next to null before adding
• Appending new node without deleting last node
• Confusing node values or order