LeetCode 692. Top K Frequent Words

题目

Given a non-empty list of words, return the k most frequent elements.

Your answer should be sorted by frequency from highest to lowest. If two words have the same frequency, then the word with the lower alphabetical order comes first.

Example 1:

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Input: ["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: [“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.

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**Note:**
- You may assume k is always valid, 1 ≤ k ≤ number of unique elements.
- Input words contain only lowercase letters.
**Follow up:**
- Try to solve it in O(n log k) time and O(n) extra space.
## 分析
和 topk frequent element 一样的
## 代码

import heapq

Uses a dict to maintain counts, heapifys the list of counts, then selects K elements out of the max heap.

O(n + klogn)

class Solution(object):
def topKFrequent(self, words, k):
“””
:type nums: List[str]
:type k: int
:rtype: List[str]
“””
freq = {}
freq_list=[]
for word in words:
if word in freq:
freq[word] = freq[word] + 1
else:
freq[word] = 1

for key in freq.keys():

    freq_list.append((-freq[key], key))
heapq.heapify(freq_list)
topk = []
for i in range(0,k):
    topk.append(heapq.heappop(freq_list)[1])
return topk        

```

点评

和 topk frequent element 一样的