Array Declaration and Initialization in DSA Python - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Array Initialization with List Multiplication

What is the output of the following Python code that initializes a 2D array using list multiplication and then modifies one element?

DSA Python

arr = [[0]*3]*3
arr[0][0] = 1
print(arr)

A [[1, 0, 0], [1, 0, 0], [1, 0, 0]]

B [[1, 0, 0], [0, 0, 0], [0, 0, 0]]

C [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

D SyntaxError

💡 Hint

Think about how list multiplication affects inner lists and references.

Using [[0]*3]*3 creates three references to the same inner list. Changing one element affects all rows.

❓ Predict Output

intermediate

Output of Array Initialization Using List Comprehension

What is the output of this Python code that initializes a 2D array using list comprehension and modifies one element?

DSA Python

arr = [[0 for _ in range(3)] for _ in range(3)]
arr[0][0] = 1
print(arr)

A [[1, 0, 0], [0, 0, 0], [0, 0, 0]]

B [[1, 0, 0], [1, 0, 0], [1, 0, 0]]

C [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

D TypeError

💡 Hint

List comprehension creates independent inner lists.

Each inner list is a separate object, so changing one element affects only that row.

🧠 Conceptual

advanced

Understanding Array Initialization Behavior

Why does using arr = [[0]*3]*3 cause unexpected behavior when modifying elements in a 2D array?

A Because it creates a 3x3 array with independent inner lists.

B Because it initializes the array with zeros incorrectly.

C Because it creates multiple references to the same inner list, so changes affect all rows.

D Because Python does not support 2D arrays.

💡 Hint

Think about how list multiplication works with nested lists.

List multiplication copies references, not the objects themselves, causing all rows to point to the same list.

❓ Predict Output

advanced

Output of Array Initialization with Mixed Types

What is the output of this Python code that initializes an array with mixed types and prints it?

DSA Python

arr = [1, 'two', 3.0, [4], (5,)]
print(arr)

A [1, 2, 3, 4, 5]

B [1, 'two', 3.0, 4, 5]

C TypeError

D [1, 'two', 3.0, [4], (5,)]

💡 Hint

Python lists can hold different data types together.

Python lists can contain elements of different types including integers, strings, floats, lists, and tuples.

🔧 Debug

expert

Identify the Error in Array Initialization

What error does the following Python code raise when trying to initialize an array?

DSA Python

arr = [0]*3
arr[3] = 1
print(arr)

A SyntaxError

B IndexError

C TypeError

D No error, prints [0, 0, 0, 1]

💡 Hint

Check the valid indices for the list.

The list has indices 0, 1, 2. Accessing index 3 is out of range and raises IndexError.