https://leetcode.com/problems/group-anagrams/description/

시간 복잡도 : O(n * klogk)
이게 맞나?
output = {}
for string in strs:
sorted_str = str(sorted(string))
if sorted_str in output:
output[sorted_str].append(string)
else:
output[sorted_str] = [string]
return output.values()