题目
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.
难度
Medium
方法
对每个字符次数统计，排序后组成新的字符串即可。借用python的Counter和most_common()方法，非常简单
python代码
import collections
class Solution(object):
def frequencySort(self, s):
"""
:type s: str
:rtype: str
"""
return "".join([char*times for char, times in collections.Counter(s).most_common()])
assert Solution().frequencySort("ttreee") == "eeettr"
