Given two binary strings, return their sum (also a binary string).
The input strings are both non-empty and contains only characters 1 or 0.
Example 1:
Input: a = "11", b = "1" Output: "100"
Example 2:
Input: a = "1010", b = "1011" Output: "10101"
[leetcode]67. Add Binary 二进制加法
原文：https://www.cnblogs.com/liuliu5151/p/9808258.html