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?