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"

Solution: Using two pointer

We use the carray to store the temp sum and then update the current bit and carray.

    string addBinary(string a, string b) {
        string ans = "";
        int n = a.size()-1, m = b.size()-1, carry = 0;
        while (n < a.size() || m < b.size()) {
            if (n < a.size()) carry += a[n--] - '0';
            if (m < b.size()) carry += b[m--] - '0';

            ans = to_string(carry % 2) + ans;
            carry = carry / 2;
        }
        return carry == 1 ? '1' + ans : ans;
    }