67. Add Binary

Given two binary strings a and b, return their sum as a binary string.

Example 1:
Input: a = "11", b = "1"
Output: "100"

Example 2:
Input: a = "1010", b = "1011"
Output: "10101"

Constraints:

• 1 <= a.length, b.length <= 10^4
• a and b consist only of '0' or '1' characters.
• Each string does not contain leading zeros except for the zero itself.

Solution in python:

class Solution:
    def addBinary(self, a: str, b: str) -> str:
        lena = len(a)
        lenb = len(b)

        if lena < lenb:
            a = "0" * (lenb - lena) + a
            max_len = lenb
        else:
            b = "0" * (lena - lenb) + b
            max_len = lena
        c = ""
        carry = 0
        for i in range(max_len-1, -1, -1):
            temp = (int(a[i]) + int(b[i]) + carry)
            if temp >= 2:
                c = str(temp - 2) + c
                carry = 1
            else:
                c = str(temp) + c
                carry = 0
        if carry:
            c = "1" + c
        return c