How should I practice Select First or Last K Stream Words?

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Problem · Array

● Medium

GoogleNEW GRADPHONE SCREEN

You are given a finite stream of lowercase words, an integer k, and one of four modes:

FIRST: return the first k words.
LAST: return the last k words.
FIRST_DISTINCT: scan from left to right and return the first k different words, keeping their first-occurrence order.
LAST_DISTINCT: keep at most one copy of each word, select the k words whose final occurrences are latest, and return them in the order of those final occurrences.

For a distinct mode, if the stream contains fewer than k different words, return all different words in the required order.

selectStreamWords(words: String[], k: int, mode: String) → String[]

words = ["ant","bee","ant","cat","dog"]k = 2mode = "FIRST"return = ["ant","bee"]

The first two stream items are returned, including any repetitions that would occur there.

words = ["ant","bee","ant","cat","dog"]k = 3mode = "LAST"return = ["ant","cat","dog"]

The final three arrivals occupy indices 2 through 4.

words = ["ant","bee","ant","cat","bee"]k = 3mode = "LAST_DISTINCT"return = ["ant","cat","bee"]

The final occurrences of ant, cat, and bee are at indices 2, 3, and 4, respectively.