Array Deletion at Middle Index in DSA Python - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output after deleting middle element from an odd-length array

What is the output of the following code after deleting the middle element from the array?

DSA Python

arr = [10, 20, 30, 40, 50]
mid = len(arr) // 2
arr.pop(mid)
print(arr)

A [10, 30, 40, 50]

B [10, 20, 30, 40]

C [20, 30, 40, 50]

D [10, 20, 40, 50]

💡 Hint

Remember that integer division // gives the middle index for odd-length arrays.

The middle index for the array of length 5 is 2 (0-based). Removing element at index 2 removes 30, so the array becomes [10, 20, 40, 50].

❓ Predict Output

intermediate

Output after deleting middle element from an even-length array

What is the output of the following code after deleting the middle element from the array?

DSA Python

arr = [5, 15, 25, 35, 45, 55]
mid = len(arr) // 2
arr.pop(mid)
print(arr)

A [5, 15, 25, 45, 55]

B [15, 25, 35, 45, 55]

C [5, 15, 25, 35, 45]

D [5, 15, 35, 45, 55]

💡 Hint

For even length, integer division picks the higher middle index.

The length is 6, so mid = 3. Removing element at index 3 removes 35, so the array becomes [5, 15, 25, 45, 55].

🔧 Debug

advanced

Identify the error in deleting middle element

What error will this code produce when trying to delete the middle element?

DSA Python

arr = [1, 2, 3, 4]
mid = len(arr) / 2
arr.pop(mid)
print(arr)

A IndexError: pop index out of range

B SyntaxError: invalid syntax

C TypeError: 'float' object cannot be interpreted as an integer

D No error, output: [1, 2, 4]

💡 Hint

Check the type of mid and what pop expects as index.

len(arr) / 2 returns a float (2.0). pop() requires an integer index, so passing a float causes a TypeError.

🧠 Conceptual

advanced

Effect of deleting middle element on array length

If an array has 7 elements, what will be its length after deleting the middle element?

A 7

B 6

C 5

D 8

💡 Hint

Deleting one element reduces length by one.

Deleting one element from 7 elements leaves 6 elements.

❓ Predict Output

expert

Output after deleting middle element in a loop

What is the final output of the code after deleting the middle element repeatedly until the array is empty?

DSA Python

arr = [1, 2, 3, 4, 5]
while arr:
    mid = len(arr) // 2
    arr.pop(mid)
print(arr)

A []

B [3]

C [2]

D [1]

💡 Hint

Each loop removes the middle element until no elements remain.

The loop removes the middle element repeatedly until the array is empty, so the final output is an empty list [].

Practice

1. What happens when you delete the middle element from an array with an odd number of elements?

easy

A. The element at the exact middle index is removed, and the array size decreases by one.

B. The first element is removed instead of the middle one.

C. The array size remains the same but the middle element is set to zero.

D. The last element is removed instead of the middle one.

Solution

1. Step 1: Identify the middle index in an odd-length array

   For an array with odd length n, the middle index is n//2 (integer division).

2. Step 2: Remove the element at the middle index

   Deleting the element at this index reduces the array size by one and shifts elements after it left.

3. Final Answer:

   The element at the exact middle index is removed, and the array size decreases by one. -> Option A

4. Quick Check:

   Middle element removed = The element at the exact middle index is removed, and the array size decreases by one. [OK]

Hint: Middle index = length // 2 for odd arrays [OK]

Common Mistakes:

• Removing first or last element instead of middle
• Not reducing array size after deletion
• Confusing middle index calculation

2. Which of the following Python statements correctly deletes the middle element from a list named arr with odd length?

easy

A. arr.pop(len(arr))

B. del arr[len(arr)//2]

C. arr.remove(len(arr)//2)

D. arr.delete(len(arr)//2)

Solution

1. Step 1: Understand Python deletion syntax

   The del statement removes an element at a specific index from a list.

2. Step 2: Calculate middle index and delete

   Using len(arr)//2 gives the middle index for odd length. So del arr[len(arr)//2] deletes the middle element correctly.

3. Final Answer:

   del arr[len(arr)//2] -> Option B

4. Quick Check:

   Correct syntax for deletion = del arr[len(arr)//2] [OK]

Hint: Use del with index: del arr[len(arr)//2] [OK]

Common Mistakes:

• Using remove() which deletes by value, not index
• Using pop() with wrong index
• Using non-existent delete() method

3. What is the output of the following code?

arr = [10, 20, 30, 40, 50]
del arr[len(arr)//2]
print(arr)

medium

A. [10, 30, 40, 50]

B. [10, 20, 30, 40]

C. [20, 30, 40, 50]

D. [10, 20, 40, 50]

Solution

1. Step 1: Calculate middle index

   Length of arr is 5, so middle index = 5 // 2 = 2.

2. Step 2: Delete element at index 2 and print

   Element at index 2 is 30. After deletion, arr becomes [10, 20, 40, 50].

3. Final Answer:

   [10, 20, 40, 50] -> Option D

4. Quick Check:

   Deleted arr[2] = 30, remaining = [10, 20, 40, 50] [OK]

Hint: Middle index 2 in 5 elements; delete arr[2] [OK]

Common Mistakes:

• Deleting wrong index (like 3 or 1)
• Confusing element value with index
• Printing before deletion

4. The following code is intended to delete the middle element from an array arr. What is the error?

arr = [1, 2, 3, 4, 5]
arr.remove(len(arr)//2)
print(arr)

medium

A. It deletes the last element instead of the middle one.

B. It causes an IndexError because remove expects an index.

C. It deletes the element with value 2 instead of the middle index element.

D. There is no error; it deletes the middle element correctly.

Solution

1. Step 1: Understand remove() method behavior

   remove(x) deletes the first element with value x, not at index x.

2. Step 2: Analyze the argument passed to remove()

   len(arr)//2 = 5//2 = 2, so arr.remove(2) deletes element with value 2, not element at index 2.

3. Final Answer:

   It deletes the element with value 2 instead of the middle index element. -> Option C

4. Quick Check:

   remove deletes by value, not index = It deletes the element with value 2 instead of the middle index element. [OK]

Hint: remove() deletes by value, del deletes by index [OK]

Common Mistakes:

• Confusing remove() with del or pop()
• Expecting remove() to delete by index
• Not calculating middle index correctly

5. Given an array arr = [5, 10, 15, 20, 25, 30] with even length, which code correctly deletes the middle element(s) so that after deletion the array is [5, 10, 25, 30]?

hard

A. del arr[len(arr)//2 - 1]; del arr[len(arr)//2]

B. del arr[len(arr)//2]; del arr[len(arr)//2 - 1]

C. arr.pop(len(arr)//2); arr.pop(len(arr)//2 - 1)

D. arr.remove(len(arr)//2); arr.remove(len(arr)//2 - 1)

Solution

1. Step 1: Identify middle indices for even length array

   Length is 6, middle indices are 2 and 3 (0-based), values 15 and 20.

2. Step 2: Delete elements at indices 2 and 3 accounting for length change

   del arr[len(arr)//2 - 1] deletes index 2 (15), array becomes [5, 10, 20, 25, 30]. Then del arr[len(arr)//2] deletes new index 2 (20), resulting in [5, 10, 25, 30].

3. Final Answer:

   del arr[len(arr)//2 - 1]; del arr[len(arr)//2] -> Option A

4. Quick Check:

   del arr[2] then del arr[2] (after shift) = [5, 10, 25, 30] [OK]

Hint: For even length, delete lower middle index first then the new middle index [OK]

Common Mistakes:

• Deleting higher index first without adjusting for length change
• Using pop() in wrong order causing incorrect shifts
• Using remove() which deletes by value