692 Top K Frequent Words

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]]

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

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class Pair:
    def __init__(self, word, freq):
        self.word = word
        self.freq = freq
    def __lt__(self, p):
        return (
            self.freq < p.freq
            or (self.freq == p.freq and self.word > p.word)
        )

class Solution:
    def topKFrequent(self, words: List[str], k: int) -> List[str]:
        heap = []
        counts = defaultdict(int)
        for word in words:
            counts[word] += 1
        
        for word, count in counts.items():
            heapq.heappush(heap, Pair(word, count))
            if len(heap) > k:
                heapq.heappop(heap)
        return [p.word for p in sorted(heap, reverse=True)]