Array Deletion at End in DSA Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Array Deletion at End' mean?

It means removing the last element from an array, making the array one element shorter.

beginner

What happens to the array size after deleting the last element?

The size of the array decreases by one because the last element is removed.

intermediate

Why is deleting the last element in an array efficient?

Because it does not require shifting any other elements, so it takes constant time (O(1)).

beginner

Show the Python code to delete the last element from a list named 'arr'.

Use arr.pop() to remove and return the last element from the list.

intermediate

What happens if you try to delete the last element from an empty array?

It causes an error because there is no element to remove.

What is the time complexity of deleting the last element from an array?

A O(log n)

B O(n)

C O(1)

D O(n^2)

Deleting the last element is done in constant time because no shifting is needed.

Which Python method removes the last element from a list?

A remove()

B pop()

C delete()

D discard()

pop() removes and returns the last element of the list.

What happens if you call pop() on an empty list in Python?

A Raises IndexError

B Removes first element

C Returns None

D Does nothing

pop() on an empty list raises an IndexError because there is no element to remove.

After deleting the last element, what is the new last element of the array?

A The first element

B No element

C The deleted element

D The element before the deleted one

The new last element is the one before the deleted last element.

Which of these is NOT a valid reason why deleting the last element is efficient?

A It requires scanning the whole array

B It takes constant time

C No elements need to be shifted

D It directly accesses the last element

Deleting the last element does NOT require scanning the whole array.

Explain how deleting the last element from an array works and why it is efficient.

Think about what happens to the array length and other elements.

Write a simple Python code snippet to delete the last element from a list and handle the case when the list is empty.

Use pop() inside a try block and catch IndexError.

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