public String addBinary(String a, String b) {
            StringBuilder re = new StringBuilder();
            int i = a.length() - 1;
            int j = b.length() - 1;
            int carry = 0;
            while (i >= 0 || j >= 0 || carry > 0) {
                int valueA = i < 0 ? 0 : a.charAt(i) - '0';
                int valueB = j < 0 ? 0 : b.charAt(j) - '0';
                re.append((valueA + valueB + carry) % 2);
                carry = (valueA + valueB + carry) / 2;
                i--;
                j--;
            }
            return re.reverse().toString();
        }