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First and Last K Words From a Stream

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Problem statement

Words arrive in the order given by words. Return two lists: the first k retained words and the last k retained words.

If distinct is false, retain every occurrence. If distinct is true, retain only the first occurrence of each word, preserving first-occurrence order.

When fewer than k words remain, return all of them in both lists. The two returned lists may overlap.

Function

firstAndLastKWords(words: String[], k: int, distinct: boolean) → String[][]

Examples

Example 1

words = ["a","b","c","d"]k = 2distinct = falsereturn = [["a","b"],["c","d"]]

The first two and final two stream occurrences are returned.

Example 2

words = ["a","b","a","c"]k = 2distinct = truereturn = [["a","b"],["b","c"]]

The retained distinct sequence is [a,b,c].

Example 3

words = ["one"]k = 3distinct = falsereturn = [["one"],["one"]]

Only one word is available, so both results contain it.

Constraints

1 <= words.length <= 100000.
1 <= k <= 100000.
Every word has length from 1 through 100.
Words contain lowercase English letters.