Delete Node at End in DSA Python - Execution Trace

Concept Flow - Delete Node at End

Start at head

↓

Check if list empty?

Yes→Nothing to delete, EXIT

No↓

Traverse to second last node

↓

Set second last node's next to null

↓

Delete last node

↓

End

Start from the head, check if list is empty, then move to the second last node and remove the last node by updating pointers.

Execution Sample

DSA Python

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

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

Deletes the last node from a singly linked list and returns the updated head.

Execution Table

Step	Action	Current Node Data	Next Node Data	Pointer Update	List State
1	Check if head is None	1	2	No	1 -> 2 -> 3 -> None
2	Check if head.next is None	1	2	No	1 -> 2 -> 3 -> None
3	Set temp = head	1	2	No	1 -> 2 -> 3 -> None
4	Check temp.next.next exists	1	2	No	1 -> 2 -> 3 -> None
5	Move temp to temp.next	2	3	No	1 -> 2 -> 3 -> None
6	Check temp.next.next exists	2	3	No	1 -> 2 -> 3 -> None
7	temp.next.next is None, stop loop	2	3	No	1 -> 2 -> 3 -> None
8	Set temp.next = None (delete last node)	2	None	Yes	1 -> 2 -> None
9	Return head	1	2	No	1 -> 2 -> None

💡 Last node deleted by setting second last node's next to None

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 8	Final
head	Node(1)	Node(1)	Node(1)	Node(1)	Node(1)
temp	None	Node(1)	Node(2)	Node(2)	Node(2)

Key Moments - 3 Insights

Why do we check if head.next is None before traversing?

Because if head.next is None, it means there is only one node. We delete it by returning None. This is shown in execution_table row 2.

Why do we use temp.next.next in the while loop condition?

To stop at the second last node, so we can remove the last node by setting temp.next to None. This is shown in execution_table rows 4-7.

What happens if the list is empty at the start?

The function returns None immediately, meaning no deletion happens. This is shown in execution_table row 1.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of temp after step 5?

A Node with data 2

B Node with data 1

C Node with data 3

D None

💡 Hint

Check the 'Current Node Data' column at step 5 in execution_table

At which step does the last node get deleted?

A Step 4

B Step 7

C Step 8

D Step 9

💡 Hint

Look for the step where 'Pointer Update' is 'Yes' in execution_table

If the list had only one node, what would the function return?

A The same single node

B None

C A new node

D An error

💡 Hint

Refer to execution_table row 2 where head.next is None

Concept Snapshot

Delete Node at End in singly linked list:
- Check if list empty or single node
- Traverse to second last node
- Set second last node's next to None
- Last node is removed
- Return updated head

Full Transcript

This visual execution shows how to delete the last node in a singly linked list. We start by checking if the list is empty or has only one node. If empty, we return None. If only one node, we delete it by returning None. Otherwise, we traverse the list to find the second last node by checking temp.next.next. Once found, we set temp.next to None, removing the last node. The updated list is then returned. The execution table traces each step, showing variable values and list state. Key moments clarify why we check conditions and how traversal works. The quiz tests understanding of variable states and deletion step.