Array Access and Update at Index in DSA Python - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output after updating array element at index

What is the output of the following Python code after updating the element at index 2?

DSA Python

arr = [5, 10, 15, 20, 25]
arr[2] = 100
print(arr)

A [5, 10, 15, 20, 25]

B [5, 100, 15, 20, 25]

C [100, 10, 15, 20, 25]

D [5, 10, 100, 20, 25]

💡 Hint

Remember that list indices start at 0 in Python.

The element at index 2 (third element) is updated from 15 to 100. The rest remain unchanged.

❓ Predict Output

intermediate

Output after multiple updates on array

What will be printed after these updates to the array?

DSA Python

arr = [1, 2, 3, 4, 5]
arr[0] = 10
arr[4] = 50
print(arr)

A [10, 2, 3, 4, 50]

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

C [10, 2, 3, 4, 5]

D [1, 2, 3, 4, 50]

💡 Hint

Check which indices are updated and what values they get.

The first element (index 0) is changed to 10 and the last element (index 4) to 50.

🔧 Debug

advanced

Identify the error when updating an array index

What error will this code produce when run?

DSA Python

arr = [7, 8, 9]
arr[3] = 10
print(arr)

A No error, output: [7, 8, 9, 10]

B TypeError: 'int' object is not subscriptable

C IndexError: list assignment index out of range

D SyntaxError: invalid syntax

💡 Hint

Check the valid indices for the array of length 3.

Index 3 does not exist in the array of length 3 (indices 0,1,2). Trying to assign to it causes IndexError.

🧠 Conceptual

advanced

Effect of negative index update on array

What is the output after updating the array element at index -1?

DSA Python

arr = [3, 6, 9, 12]
arr[-1] = 100
print(arr)

A [100, 6, 9, 12]

B [3, 6, 9, 100]

C [3, 6, 100, 12]

D IndexError: list assignment index out of range

💡 Hint

Negative indices count from the end of the list in Python.

Index -1 refers to the last element, so it updates 12 to 100.

🚀 Application

expert

Final array after sequence of updates and accesses

Given the code below, what is the final printed array?

DSA Python

arr = [0, 1, 2, 3, 4, 5]
for i in range(2, 5):
    arr[i] = arr[i] * 2
arr[0] = arr[5] + arr[1]
print(arr)

A [6, 1, 4, 6, 8, 5]

B [5, 1, 4, 6, 8, 5]

C [6, 1, 2, 3, 4, 5]

D [0, 1, 4, 6, 8, 5]

💡 Hint

Trace each update step carefully, especially the loop and the final assignment.

Elements at indices 2,3,4 are doubled: 2->4, 3->6, 4->8. Then arr[0] = arr[5] + arr[1] = 5 + 1 = 6.