Hackerrank Algorithms 4

Question 1

What is the space complexity of a recursive Fibonacci function without memoization?

Accepted Answer

O(n)

Answer

The call stack depth reaches O(n) since each call adds one frame before returning.

Question 2

Which technique avoids recomputing overlapping subproblems by storing results in a table?

Accepted Answer

Dynamic programming

Answer

Dynamic programming uses memoization or tabulation to store and reuse subproblem solutions.

Question 3

What does `functools.lru_cache(maxsize=None)` do when applied to a recursive function?

Accepted Answer

Caches return values to avoid recomputation

Answer

`lru_cache` memoizes function call results so identical inputs return cached output instantly.

Question 4

Given `s = 'racecar'`, which one-liner checks if it is a palindrome?

Accepted Answer

s == s[::-1]

Answer

`s[::-1]` slices the string in reverse; if it equals the original, the string is a palindrome.

Question 5

What is the output of `sorted([('b', 2), ('a', 3), ('c', 1)], key=lambda x: x[1])`?

Accepted Answer

[('c', 1), ('b', 2), ('a', 3)]

Answer

Sorting by the second element (index 1) orders the tuples by their numeric values ascending.

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