Array Insertion at Middle Index in DSA Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert the value 99 at the middle index of the list.

DSA Python

arr = [1, 2, 3, 4, 5]
mid = len(arr) // 2
arr.[1](mid, 99)
print(arr)

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

Aappend

Binsert

Cextend

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using append adds the element at the end, not the middle.

Using remove deletes elements instead of adding.

The insert method adds an element at a specific index. Here, it inserts 99 at the middle index.

2fill in blank

medium

Complete the code to find the middle index of the list correctly.

DSA Python

arr = [10, 20, 30, 40, 50, 60]
mid = [1]
print(mid)

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

Alen(arr) // 2

Blen(arr) / 2

Clen(arr) % 2

Darr[len(arr)]

Attempts:

3 left

💡 Hint

Common Mistakes

Using regular division returns a float, which is invalid as a list index.

Using modulo operator does not give the middle index.

Using integer division // gives the middle index as an integer.

3fill in blank

hard

Fix the error in the code to insert 77 at the middle index of the list.

DSA Python

numbers = [5, 10, 15, 20]
middle = len(numbers) // 2
numbers.[1](middle, 77)
print(numbers)

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

Aappend

Bextend

Cinsert

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using append adds at the end, not at the middle index.

Using add or extend are invalid for this operation.

The insert method is correct to add an element at a specific index. Other methods do not accept two arguments or do not insert at an index.

4fill in blank

hard

Fill both blanks to create a list of squares for numbers less than 5 and insert 100 at the middle index.

DSA Python

nums = [1, 2, 3, 4, 5, 6]
squares = [x[1]2 for x in nums if x [2] 5]
mid = len(squares) // 2
squares.insert(mid, 100)
print(squares)

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

A**

B>

C<

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '**' does addition, not squaring.

Using '>' instead of '<' filters wrong numbers.

Use ** for exponentiation to square numbers, and < to filter numbers less than 5.

5fill in blank

hard

Fill all three blanks to create a dictionary of numbers and their squares for numbers greater than 2, then insert 50 at the middle index of the list.

DSA Python

nums = [1, 2, 3, 4, 5]
squares_dict = {{ [1]: [2] for [1] in nums if [1] [3] 2 }}
nums.insert(len(nums)//2, 50)
print(nums)
print(squares_dict)

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

Ax

Bx**2

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' filters wrong numbers.

Using the wrong variable name causes errors.

Use x as the key, x**2 as the value, and > to filter numbers greater than 2.

Practice

1. What is the middle index of an array with 7 elements when inserting a new element?

easy

A. 3

B. 4

C. 2

D. 5

Solution

1. Step 1: Calculate middle index for odd length array

   For an array of length 7, middle index = length // 2 = 7 // 2 = 3.

2. Step 2: Understand insertion position

   Inserting at index 3 places the new element exactly in the middle.

3. Final Answer:

   3 -> Option A

4. Quick Check:

   Middle index = length // 2 = 3 [OK]

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

Common Mistakes:

• Using length // 2 + 1 for middle index
• Using length // 2 - 1 for middle index
• Confusing middle index with last index

2. Which of the following Python statements correctly inserts the value 10 at the middle index of list arr = [1, 2, 3, 4]?

easy

A. arr.insert(0, 10)

B. arr.insert(len(arr), 10)

C. arr.insert(len(arr) // 2, 10)

D. arr.append(10)

Solution

1. Step 1: Calculate middle index for arr

   Length of arr is 4, middle index = 4 // 2 = 2.

2. Step 2: Use insert method at middle index

   arr.insert(2, 10) inserts 10 at index 2, which is the middle.

3. Final Answer:

   arr.insert(len(arr) // 2, 10) -> Option C

4. Quick Check:

   Use insert at middle index = len(arr)//2 [OK]

Hint: Use arr.insert(len(arr)//2, value) to insert in middle [OK]

Common Mistakes:

• Using append() which adds at end
• Using insert(len(arr), value) which adds at end
• Using insert(0, value) which adds at start

3. What will be the output of the following code?

arr = [5, 10, 15, 20]
mid = len(arr) // 2
arr.insert(mid, 12)
print(arr)

medium

A. [12, 5, 10, 15, 20]

B. [5, 10, 12, 15, 20]

C. [5, 10, 15, 12, 20]

D. [5, 10, 15, 20, 12]

Solution

1. Step 1: Calculate middle index

   Length of arr is 4, so mid = 4 // 2 = 2.

2. Step 2: Insert 12 at index 2

   arr.insert(2, 12) inserts 12 before element at index 2 (which is 15).

3. Final Answer:

   [5, 10, 12, 15, 20] -> Option B

4. Quick Check:

   Insert at mid index shifts elements right [OK]

Hint: Insert at mid index shifts elements right [OK]

Common Mistakes:

• Inserting at wrong index causing misplaced element
• Appending instead of inserting
• Confusing index with value

4. Find the error in the code below that tries to insert 99 in the middle of arr = [1, 2, 3, 4, 5]:

arr = [1, 2, 3, 4, 5]
mid = len(arr) / 2
arr.insert(mid, 99)
print(arr)

medium

A. Using '/' instead of '//' for middle index calculation

B. Using insert() instead of append() method

C. Not defining arr before insertion

D. Using print() incorrectly

Solution

1. Step 1: Check middle index calculation

   len(arr) / 2 returns a float (2.5), but insert() requires an integer index.

2. Step 2: Correct middle index calculation

   Use integer division '//' to get integer index: mid = len(arr) // 2 = 2.

3. Final Answer:

   Using '/' instead of '//' for middle index calculation -> Option A

4. Quick Check:

   Index must be int, use '//' not '/' [OK]

Hint: Use '//' for integer division to get valid index [OK]

Common Mistakes:

• Using '/' causing TypeError
• Forgetting to calculate middle index
• Using append() instead of insert()

5. Given arr = [2, 4, 6, 8, 10, 12], write code to insert the value 7 exactly in the middle so that the array remains sorted. What will be the final array?

hard

A. [2, 4, 7, 6, 8, 10, 12]

B. [2, 4, 6, 8, 7, 10, 12]

C. [7, 2, 4, 6, 8, 10, 12]

D. [2, 4, 6, 7, 8, 10, 12]

Solution

1. Step 1: Calculate middle index for even length array

   Length is 6, middle index = 6 // 2 = 3.

2. Step 2: Insert 7 at index 3 to keep array sorted

   Inserting 7 at index 3 places it between 6 and 8, maintaining sorted order.

3. Final Answer:

   [2, 4, 6, 7, 8, 10, 12] -> Option D

4. Quick Check:

   Insert 7 at middle index 3 to keep sorted [OK]

Hint: Insert at middle index to keep sorted order [OK]

Common Mistakes:

• Inserting 7 at wrong index breaking order
• Appending 7 at end
• Inserting 7 at start