Sort Characters By Frequency

Similar Problems:

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.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

## https://code.dennyzhang.com/sort-characters-by-frequency ## Baisc Ideas: Sort with customized function ## ## Complexity: import collections class Solution(object): def frequencySort(self, s): """ :type s: str :rtype: str """ m = collections.defaultdict(lambda: 0) for ch in s: m[ch] += 1 def myCompare(v1, v2): if m[v1] > m[v2]: return -1 elif m[v1] < m[v2]: return 1 else: if v1 == v2: return 0 return -1 if v1 < v2 else 1 return ''.join(sorted(s, cmp=myCompare)) # s = Solution() # print s.frequencySort("Aabb") # "bbAa"