Add Binary

Given two binary strings `a` and `b`, return their sum as a binary string. ### 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. ### Input Format - Line 1: Binary string `a`. - Line 2: Binary string `b`. ### Output Format Print the binary sum string.