LeetCode – Refresh – Add Binary

This question is pretty straight forward.

class Solution {
public:
    string addBinary(string a, string b) {
        int runnerA = a.size()-1, runnerB = b.size()-1, carry = 0;
        if (runnerA < 0) return b;
        if (runnerB < 0) return a;
        string result;
        while (runnerA >= 0 || runnerB >= 0) {
            int sum = carry;
            if (runnerA >= 0) sum += int(a[runnerA--] - '0');
            if (runnerB >= 0) sum += int(b[runnerB--] - '0');
            carry = sum/2;
            result = char(sum%2 + '0') + result;
        }
        if (carry) result = '1' + result;
        return result;
    }
};