Array Insertion at Beginning in DSA Python - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after inserting elements at the beginning?

Consider the following Python code that inserts elements at the beginning of a list. What will be printed?

DSA Python

arr = [3, 4, 5]
arr.insert(0, 2)
arr.insert(0, 1)
print(arr)

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

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

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

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

💡 Hint

Remember that insert(0, x) adds x at the start of the list.

Each insert at index 0 places the new element at the front, pushing existing elements right.

❓ Predict Output

intermediate

What is the final list after multiple insertions at the beginning?

What will be the output of this code snippet?

DSA Python

lst = []
lst.insert(0, 'c')
lst.insert(0, 'b')
lst.insert(0, 'a')
print(lst)

A ['c', 'b', 'a']

B ['c', 'a', 'b']

C ['b', 'a', 'c']

D ['a', 'b', 'c']

💡 Hint

Each insert at index 0 adds the element to the front.

Inserting 'c' first makes ['c'], then 'b' at front makes ['b','c'], then 'a' at front makes ['a','b','c'].

🔧 Debug

advanced

Why does this code not insert at the beginning as expected?

The code below is intended to insert 0 at the beginning of the list but does not work as expected. What is the problem?

DSA Python

numbers = [1, 2, 3]
numbers.append(0)
print(numbers)

A It inserts 0 at the beginning but prints the list reversed.

B It raises a TypeError because append needs two arguments.

C It adds 0 at the end, not the beginning, because append adds to the end.

D It removes the first element instead of inserting.

💡 Hint

Check what append does compared to insert.

append adds an element at the end of the list, not at the beginning. To add at the start, use insert(0, value).

❓ Predict Output

advanced

What is the output after inserting elements at the beginning in a loop?

What will be printed after running this code?

DSA Python

arr = []
for i in range(3):
    arr.insert(0, i)
print(arr)

A [2, 1, 0]

B [0, 1, 2]

C [0, 2, 1]

D [1, 2, 0]

💡 Hint

Each new element is added at the front, pushing others right.

Loop inserts 0 at front → [0], then 1 at front → [1,0], then 2 at front → [2,1,0].

🧠 Conceptual

expert

What is the time complexity of inserting an element at the beginning of a Python list?

Consider a Python list with n elements. What is the time complexity of inserting an element at the beginning using insert(0, value)?

A O(n^2) because insertion requires nested loops.

B O(n) because all elements must be shifted right to make space.

C O(log n) because Python uses binary search internally.

D O(1) because insert at index 0 is constant time.

💡 Hint

Think about what happens to existing elements when inserting at the start.

Inserting at the start requires shifting all existing elements one position to the right, which takes linear time.