## 1. Problem

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 <= 104
- a and b consist only of ‘0’ or ‘1’ characters.
- Each string does not contain leading zeros except for the zero itself.

## 2. Solution

I solve this problem like this. Using Python’s bin function, you can easily solve the problem.

```
class Solution:
def addBinary(self, a: str, b: str) -> str:
return bin(int(a,2) + int(b,2))[2:]
```