Hackerrank Python Data Structures & Algorithms 3

Question 1

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

Accepted Answer

O(n)

Answer

Inserting at index 0 requires shifting all existing elements one position right, making it O(n).

Question 2

Which Python collection type uses a hash table internally and guarantees O(1) average-case lookup?

Accepted Answer

dict

Answer

Python dicts are hash maps, providing O(1) average-case get/set operations.

Question 3

What does `collections.deque` provide that a regular list does not?

Accepted Answer

O(1) appends and pops from both ends

Answer

deque is a doubly-linked list optimized for O(1) appendleft/popleft, unlike list which is O(n) at the left end.

Question 4

Given `d = defaultdict(list)`, what happens when you access `d['new_key']`?

Accepted Answer

An empty list is created and returned

Answer

defaultdict calls the factory function (list) to create a default value when a missing key is accessed.

Question 5

Which algorithm does Python's built-in `sort()` use?

Accepted Answer

Timsort

Answer

Python uses Timsort, a hybrid of merge sort and insertion sort, with O(n log n) worst case.

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