Hackerrank Collections and Data Structures 3

Question 1

What does `Counter.subtract()` do differently from subtracting two Counters with `-`?

Accepted Answer

subtract() allows negative counts; - removes non-positive counts

Answer

`subtract()` allows counts to go to zero or negative, while the `-` operator drops non-positive counts.

Question 2

What is the maximum length constraint enforced when creating a `collections.deque` with `maxlen=3` and you append a 4th element?

Accepted Answer

The oldest element on the opposite end is discarded

Answer

When maxlen is set and the deque is full, appending to one end automatically discards an element from the other end.

Question 3

Which `collections.OrderedDict` method moves an existing key to either end?

Accepted Answer

move_to_end()

Answer

`move_to_end(key, last=True)` moves an existing key to the right end (or left end if last=False).

Question 4

What does `namedtuple._fields` return for `Point = namedtuple('Point', 'x y')`?

Accepted Answer

('x', 'y')

Answer

`_fields` is a tuple of strings listing the field names of the named tuple.

Question 5

How does `collections.ChainMap` handle key lookups when the same key exists in multiple maps?

Accepted Answer

Returns the value from the first map where the key is found

Answer

ChainMap searches through the maps in order and returns the first match found.

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