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.
Subscribe to see which companies asked this question.對python來說 就是dcit的排序問題
class Solution(object):    def frequencySort(self, s):        d = {}                for i in s:            d[i] = d.get(i,0) + 1                    l = sorted(d.iteritems(),key = lambda k:k[1],reverse = True)                res = ''        for (k,v) in l:            res += k * v        return res                """        :type s: str        :rtype: str        """