692\. Top K Frequent Words

Medium

Given an array of strings `words` and an integer `k`, return _the_ `k` _most frequent strings_.

Return the answer **sorted** by **the frequency** from highest to lowest. Sort the words with the same frequency by their **lexicographical order**.

**Example 1:**

**Input:** words = ["i","love","leetcode","i","love","coding"], k = 2

**Output:** ["i","love"]

**Explanation:** "i" and "love" are the two most frequent words. Note that "i" comes before "love" due to a lower alphabetical order. 

**Example 2:**

**Input:** words = ["the","day","is","sunny","the","the","the","sunny","is","is"], k = 4

**Output:** ["the","is","sunny","day"]

**Explanation:** "the", "is", "sunny" and "day" are the four most frequent words, with the number of occurrence being 4, 3, 2 and 1 respectively. 

**Constraints:**

*   `1 <= words.length <= 500`
*   `1 <= words[i] <= 10`
*   `words[i]` consists of lowercase English letters.
*   `k` is in the range `[1, The number of **unique** words[i]]`

**Follow-up:** Could you solve it in `O(n log(k))` time and `O(n)` extra space?