You are given two strings a and b. Each one is a number written in binary, so it uses only the digits 0 and 1.
Add the two numbers. Return the sum as a binary string.
Examples
Example 1:
Input: a = "101", b = "110"
Output: "1011"
Explanation: "101" is 5 and "110" is 6. The sum is 11, which is "1011" in binary.
Example 2:
Input: a = "11", b = "11"
Output: "110"
Explanation: "11" is 3. 3 + 3 = 6, which is "110" in binary.
Example 3:
Input: a = "1011", b = "111"
Output: "10010"
Explanation: "1011" is 11 and "111" is 7. The sum is 18, which is "10010" in binary.