LeetCode 692 Top K Frequent Words

LeetCode

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?

题目大意：

求k个最高频率的单词

解题思路：

N/A

解题步骤：

N/A

注意事项：

1. 若频率一样，就按字母顺序lexicographical. 所以用大小为k的heap做比较困难。直接用排序即可

Python代码：

def topKFrequent(self, words: List[str], k: int) -> List[str]:
	freq_dict = collections.Counter(words)
	li = [(freq, word) for word, freq in freq_dict.items()]
	li.sort(key=lambda x : (-x[0], x[1]))
	return [pair[1] for pair in li[:k]]

算法分析：

时间复杂度为O(nlogn)，空间复杂度O(n)