Given a list of words, return the top k frequently occurring words.

CountingWords.kt

/*
Given an array of strings words and an integer k, return the k most frequent strings.
["i","love","leetcode","i","love","coding"], k = 2
Output: ["i","love"]
* */
fun topKFrequent(words: Array<String>, k: Int): List<String> {
    return words.groupingBy { it }.eachCount()
        .toList()
        .sortedBy { (s, _) -> s }
        .sortedByDescending { (_, v) -> v }
        .map { it.first }
        .take(k)
}