BinaryAdd.py

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

For example,
a = "11"
b = "1"
Return "100".
'''
def add_binary(str1,str2):
 '''
 Args: two binary_string
 Return: sum of the two binary strings in binary
 '''
 # sum of the two binary strings
 total = []
 
 max_len = max(len(str1), len(str2))
 # fill the string with zeros to make the two strings same length
 # turn the string to list and reverse it
 list1 = list(str1.zfill(max_len))
 list1.reverse()
 list2 = list(str2.zfill(max_len))
 list2.reverse()
 
 carry = 0
 for i in range(max_len):
 # sum for this bit
 bit_sum = int(list1[i])+ int(list2[i]) + carry
 total.append(str(bit_sum % 2))
 if bit_sum >= 2:
 carry = 1
 
 if carry == 1:
 total.append('1')
 
 total.reverse() 
 
 return ''.join(total)