【python3】leetcode 451. Sort Characters By Frequency (Medium)

451. Sort Characters By Frequency (Medium)

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

Example 1:

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.

 

Example 2:

Input:
"cccaaa"

Output:
"cccaaa"

Explanation:
Both 'c' and 'a' appear three times, so "aaaccc" is also a valid answer.
Note that "cacaca" is incorrect, as the same characters must be together.

 

Example 3:

Input:
"Aabb"

Output:
"bbAa"

Explanation:
"bbaA" is also a valid answer, but "Aabb" is incorrect.
Note that 'A' and 'a' are treated as two different characters.

class Solution:
    def frequencySort(self, s):
        """
        :type s: str
        :rtype: str
        """
        count = collections.Counter(s)
        count = collections.OrderedDict(sorted(count.items(),key=lambda t:t[1]))
        ss = ""
        for c,num in count.items():
            ss = c * num + ss
        return ss
        

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