Leetcode 67: Add Binary

 

Code

class Solution(object):
    def addBinary(self, a, b):
        """
        :type a: str
        :type b: str
        :rtype: str
        """
        if len(b) > len(a):
            a, b = b, a
        b = '0' * (len(a)-len(b)) + b

        carry = 0
        res = ['0'] * (len(a))

        for idx, (i,j) in enumerate(zip(a[::-1], b[::-1])):
            tmp = i + j + carry
            if tmp < 2:
                res[-idx-1] = str(tmp)   
            else:
                res[-idx-1] = str(tmp % 2)
                carry = 1

        # result cannot be longer than len(a)+1
        if carry:
            return str(carry) + ''.join(res)
        else:
            return ''.join(res)

 

 

Idea

From right to left, add each position.