451. Sort Characters By Frequency

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

就是按频数来排序呗！！

我的做法是先写成字典，然后用sorted和zip函数一起对字典的value进行排序。

class Solution(object):
def frequencySort(self, s):
"""
:type s: str
:rtype: str
"""
d={}
for i in s:
d[i]=d.get(i,0)+1
mylist=sorted(zip(d.values(),d.keys()),reverse=True)
s=''
for k in mylist:
s+=k[1]*k[0]
return s