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].length <= 10

• words[i]?consists of lowercase English letters.

• k?is in the range?[1, The number of?unique?words[i]]

map 跟list的聯(lián)動(dòng)，以前遇到過類似這個(gè)問題，老是記不住。。。

Runtime:?6 ms, faster than?83.47%?of?Java?online submissions for?Top K Frequent Words.

Memory Usage:?43.2 MB, less than?16.63%?of?Java?online submissions for?Top K Frequent Words.