Array Deletion at End in DSA Python - Execution Trace

Concept Flow - Array Deletion at End

Start with array

↓

Check if array is empty?

Yes→Stop: nothing to delete

No↓

Remove last element

↓

Update array size

↓

Done

This flow shows checking if the array is empty, then removing the last element and updating the size.

Execution Sample

DSA Python

arr = [10, 20, 30, 40]
if len(arr) > 0:
    arr.pop()
print(arr)

Deletes the last element from the array if it is not empty, then prints the updated array.

Execution Table

Step	Operation	Array Before	Array After	Pointer Changes	Visual State
1	Start	[10, 20, 30, 40]	[10, 20, 30, 40]	head -> index 0, tail -> index 3	10 -> 20 -> 30 -> 40 -> null
2	Check if empty	[10, 20, 30, 40]	[10, 20, 30, 40]	tail index 3 valid	10 -> 20 -> 30 -> 40 -> null
3	Remove last element	[10, 20, 30, 40]	[10, 20, 30]	tail moves from index 3 to 2	10 -> 20 -> 30 -> null
4	Update size	[10, 20, 30]	[10, 20, 30]	size = 3	10 -> 20 -> 30 -> null
5	Print array	[10, 20, 30]	[10, 20, 30]	no pointer change	10 -> 20 -> 30 -> null
6	End	[10, 20, 30]	[10, 20, 30]	final state	10 -> 20 -> 30 -> null

💡 Stop after last element removed and array size updated.

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
arr	[10, 20, 30, 40]	[10, 20, 30]	[10, 20, 30]	[10, 20, 30]
size	4	3	3	3
tail index	3	2	2	2

Key Moments - 3 Insights

Why do we check if the array is empty before deleting?

Because deleting from an empty array would cause an error. See execution_table step 2 where we check size before removal.

What happens to the array size after deletion?

The size decreases by one after removing the last element, as shown in execution_table step 4 and variable_tracker for 'size'.

How does the 'tail' pointer change after deletion?

The tail pointer moves one position left to the new last element, shown in execution_table step 3 and variable_tracker 'tail index'.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the array after removing the last element?

A [10, 20, 30]

B [10, 20, 30, 40]

C [20, 30, 40]

D []

💡 Hint

Check the 'Array After' column in step 3 of execution_table.

At which step does the tail pointer move to index 2?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Pointer Changes' column in execution_table step 3.

If the array was empty at start, what would happen at step 2?

A Remove last element anyway

B Throw error

C Stop deletion, no change

D Add a new element

💡 Hint

Refer to concept_flow and execution_table step 2 about empty array check.

Concept Snapshot

Array Deletion at End:
- Check if array is empty before deleting
- Remove last element using pop()
- Update size and tail pointer
- Resulting array has one less element
- Safe deletion avoids errors on empty array

Full Transcript

This visual trace shows how to delete the last element from an array. First, we check if the array is empty to avoid errors. If not empty, we remove the last element, update the size and tail pointer to reflect the new end of the array. The final array is printed showing the updated state. Key points include checking emptiness, pointer updates, and size decrement.

Practice

1. What happens when you delete the last element from an array in Python using pop()?

easy

A. The first element is removed and the array size stays the same.

B. The last element is removed and the array size decreases by one.

C. The array is cleared completely.

D. The array becomes empty but elements remain.

Solution

1. Step 1: Understand the pop() method

   The pop() method removes the last element from the array (list) by default.

2. Step 2: Effect on array size

   After removal, the array size decreases by one because one element is deleted.

3. Final Answer:

   The last element is removed and the array size decreases by one. -> Option B

4. Quick Check:

   pop() removes last element [OK]

Hint: pop() removes last item and shrinks array [OK]

Common Mistakes:

• Thinking pop() removes the first element
• Assuming pop() clears the whole array
• Believing array size stays the same after pop()

2. Which of the following is the correct syntax to delete the last element from a list named arr in Python?

easy

A. arr.pop()

B. arr.delete()

C. pop(arr)

D. arr.remove_last()

Solution

1. Step 1: Identify the correct method for deletion at end

   In Python, pop() is the method used to remove the last element from a list.

2. Step 2: Check syntax correctness

   The correct syntax is arr.pop(). Other options are invalid or do not exist in Python.

3. Final Answer:

   arr.pop() -> Option A

4. Quick Check:

   pop() is correct syntax [OK]

Hint: Use arr.pop() to remove last element [OK]

Common Mistakes:

• Using arr.delete() which is invalid
• Trying pop(arr) instead of arr.pop()
• Using arr.remove_last() which does not exist

3. What is the output of the following code?

arr = [10, 20, 30, 40]
arr.pop()
print(arr)

medium

A. [10, 20, 30]

B. [20, 30, 40]

C. [10, 20, 30, 40]

D. [10, 20, 40]

Solution

1. Step 1: Understand pop() effect on arr

   The pop() removes the last element, which is 40.

2. Step 2: Print the updated array

   After removal, the array becomes [10, 20, 30].

3. Final Answer:

   [10, 20, 30] -> Option A

4. Quick Check:

   Last element removed, array shrinks [OK]

Hint: pop() removes last element, print updated list [OK]

Common Mistakes:

• Expecting original array unchanged
• Removing first element instead of last
• Confusing pop() with remove()

4. Find the error in the following code that tries to delete the last element from arr:

arr = [1, 2, 3]
arr.pop(0)
print(arr)

medium

A. pop() deletes the entire array

B. pop() cannot take any arguments

C. pop() should be replaced with remove()

D. pop(0) removes the first element, not the last

Solution

1. Step 1: Analyze pop(0) usage

   pop(0) removes the element at index 0, which is the first element, not the last.

2. Step 2: Identify correct method to delete last element

   To delete the last element, pop() should be called without arguments.

3. Final Answer:

   pop(0) removes the first element, not the last -> Option D

4. Quick Check:

   pop(index) removes element at index [OK]

Hint: pop() without argument removes last element [OK]

Common Mistakes:

• Assuming pop() cannot take arguments
• Using pop(0) to remove last element
• Confusing pop() with remove()

5. Given the list arr = [5, 10, 15, 20, 25], you want to remove the last two elements using pop(). Which code snippet correctly achieves this?

hard

A. arr.pop(1)
arr.pop(0)

B. arr.pop(3)
arr.pop(2)

C. arr.pop()
arr.pop()

D. arr.pop(0)
arr.pop(1)

Solution

1. Step 1: Understand pop() without argument

   Calling pop() without arguments removes the last element each time.

2. Step 2: Apply pop() twice to remove last two elements

   Calling arr.pop() twice removes 25 then 20, the last two elements.

3. Step 3: Check other options

   Options A, B, and C use indices that become invalid or remove wrong elements after first pop.

4. Final Answer:

   arr.pop() followed by arr.pop() -> Option C

5. Quick Check:

   pop() twice removes last two elements [OK]

Hint: Use pop() twice to remove last two elements [OK]

Common Mistakes:

• Using pop() with fixed indices without updating
• Removing first elements instead of last
• Assuming pop() clears multiple elements at once