[LeetCode]Sort Characters By Frequency@Python

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Sort Characters By Frequency

Given a string, sort it in decreasing order based on the frequency of characters.

Example

Input:
“tree”

Output:
“eert”

Explanation:
‘e’ appears twice while ‘r’ and ‘t’ both appear once.
So ‘e’ must appear before both ‘r’ and ‘t’. Therefore “eetr” is also a valid answer.

Solution

复制代码

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import collections
class Solution:
    def frequencySort(self, s: str) -> str:
        dic = collections.defaultdict(int)
        for k in s:
            dic[k]+=1
        heap = [(-n, v) for v,n in dic.items()]
        heapq.heapify(heap)
        ret = ''
        while heap:
            n,v = heapq.heappop(heap)
            ret += (-n)*v
        return ret