'''

Given two binary strings, return their sum (also a binary string).

For example,

a = "11"

b = "1"

Return "100".

'''

class Solution(object):

def addBinary(self, a, b):

lenA, lenB = len(a), len(b)

a, b = list(a), list(b)

if lenA == 0:

return b

if lenB == 0:

return a

carry, r = 0, ['']*(max(lenA, lenB)+1)

for i in range(len(r)):

p1, p2 = 0, 0

if i < lenA:

p1 = int(a[lenA-1-i])

if i < lenB:

p2 = int(b[lenB-1-i])

sum = p1 + p2 + carry

r[len(r)-1-i] = str(sum%2)

carry = sum // 2

return str(int("".join(r)))

s = Solution()

print(s.addBinary('10110', '101'))