Array Insertion at Middle Index in DSA Python - Build from Scratch

Array Insertion at Middle Index

📖 Scenario: You are managing a list of daily tasks. Sometimes, you want to add a new task right in the middle of your current list to keep things balanced.

🎯 Goal: Learn how to insert a new item exactly in the middle of an existing list (array) in Python.

📋 What You'll Learn

Create a list called tasks with specific task names

Create a variable called new_task with a given task name

Insert new_task into the middle index of tasks

Print the updated tasks list

💡 Why This Matters

🌍 Real World

In daily task management apps, inserting tasks in the middle helps keep the schedule balanced and organized.

💼 Career

Understanding list operations like insertion is essential for software developers working with data collections and user interfaces.

1

Create the initial list of tasks

Create a list called tasks with these exact strings in order: 'Email', 'Meeting', 'Coding', 'Review', 'Deploy'

DSA Python

# Create the list called tasks with the given tasks
# Your code here

Hint

Use square brackets [] to create a list and separate items with commas.

2

Create the new task to insert

Create a variable called new_task and set it to the string 'Lunch Break'

DSA Python

tasks = ['Email', 'Meeting', 'Coding', 'Review', 'Deploy']
# Create the variable new_task with value 'Lunch Break'
# Your code here

Hint

Use the assignment operator = to set the variable.

3

Insert the new task in the middle

Calculate the middle index of tasks using len(tasks) // 2 and insert new_task at that index using tasks.insert()

DSA Python

tasks = ['Email', 'Meeting', 'Coding', 'Review', 'Deploy']
new_task = 'Lunch Break'
# Insert new_task into the middle index of tasks
# Your code here

Hint

Use len() to get the list length and insert() to add the item.

4

Print the updated tasks list

Print the tasks list to show the new order after insertion

DSA Python

tasks = ['Email', 'Meeting', 'Coding', 'Review', 'Deploy']
new_task = 'Lunch Break'
middle_index = len(tasks) // 2
tasks.insert(middle_index, new_task)
# Print the tasks list
# Your code here

Hint

Use print(tasks) to display the list.

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