For strings A, B, when len(A) > len(B), the longest possible subsequence of either A or B is A, and no subsequence of B can be equal to A. Answer: len(A).
When len(A) == len(B), the only subsequence of B equal to A is B; so as long as A != B, the answer remains len(A).
When A == B, any subsequence of A can be found in B and vice versa, so the answer is -1.
class Solution(object):
def findLUSlength(self, a, b):
"""
:type a: str
:type b: str
:rtype: int
"""
if a == b:
return -
1
else:
return max(len(a),len(b))
