字典存储 字典排序 遍历排序后的list
class Solution:
def frequencySort(self, s):
"""
:type s: str
:rtype: str
"""
dict1={}
for c in s:
if c in dict1:
dict1[c]+=1
else:
dict1[c]=1
b=sorted(dict1.items(),key=lambda x:x[1],reverse=True)
res=''
for item in b:
res+=item[0]*item[1]
return res