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# 67. Add Binary

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"
```

**Constraints:**

* Each string consists only of `'0'` or `'1'` characters.
* `1 <= a.length, b.length <= 10^4`
* Each string is either `"0"` or doesn't contain any leading zero.

```
# @param {String} a
# @param {String} b
# @return {String}
def add_binary(a, b)
  (a.to_i(2) + b.to_i(2)).to_s(2)
end
```