Hackerrank Algorithms 5

Question 1

Which Python data structure is ideal for BFS (breadth-first search) due to O(1) append and popleft?

Accepted Answer

collections.deque

Answer

`collections.deque` supports O(1) operations on both ends, making it efficient as a BFS queue.

Question 2

What is the time complexity of inserting an element into a Python `heapq` (min-heap)?

Accepted Answer

O(log n)

Answer

Heap insertion (heappush) requires at most log n comparisons to restore the heap property.

Question 3

What does the following return: `max([3, 1, 4, 1, 5], key=lambda x: -x)`?

Accepted Answer

1

Answer

Using `-x` as the key inverts comparisons, so `max` finds the element with the largest negative value, which is the smallest element (1).

Question 4

In the context of graph algorithms, what does DFS stand for and what data structure does it use?

Accepted Answer

Depth-First Search, stack

Answer

DFS explores as deep as possible before backtracking, using a stack (or recursion call stack) to track the path.

Question 5

What is the output of `list(zip([1,2,3], ['a','b']))`?

Accepted Answer

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

Answer

`zip` stops at the shortest iterable, so only two pairs are produced.

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