67-add-binary.cpp

class Solution {
public:
    string addBinary(string a, string b) {
        int i = a.length() - 1;
        int j = b.length() - 1;
        
        string result = "";
        int sum = 0;
        int carry = 0;
        while(i >= 0 || j >= 0) {
            sum = carry;
            if(i >= 0) sum += a[i--] - '0';
            if(j >= 0) sum += b[j--] - '0';
            carry = (sum > 1 ? 1 : 0);
            result += to_string(sum % 2);
        }
        if(carry) result += to_string(carry);
        reverse(result.begin(), result.end());
        
        return result;
    }
};