PYTHON 5A

from collections import defaultdict
str="onemissisipi"
str=sorted(str)
d={}
aux={}
for i in str:
    d[i]=str.count(i)
print(d)
print(sorted(d.values(),reverse=True))
dd={}
for k,v in d.items():
    (dd.setdefault(v,[]).append(k)
aux=dict((i,dd[i]) for i in sorted(dd.keys()))
print(aux)