Q2ThreeOdd.java

package comp1110.exam;


public class Q2ThreeOdd {

    /**
     * Input to the method is a string.
     * <p>
     * Return the sum of the even-valued digits if the string represents
     * a ThreeOdd number
     * <p>
     * Return the sum of the odd-valued digits if the string represents
     * a number that is not a ThreeOdd number.
     * <p>
     * In any other case (for example, if the input string empty or does
     * not represent a number) return -1.
     * <p>
     * A ThreeOdd number is defined by the following rules:
     * a) is a non-negative integer (may have one or more leading zeros,
     * e.g., 00303 is equivalent to 303);
     * b) is odd and divisible by three;
     * c) after removing the first and last digits, the remaining digits
     * are still a ThreeOdd number, or an empty string.
     * <p>
     * Examples of ThreeOdd numbers: "3333", "96333", "39363", "6993", "3",
     * "69". As these are ThreeOdd numbers this method should return 0, 12,
     * 6, 18, 0, 0, respectively.
     * <p>
     * Examples that are NOT ThreeOdd numbers: "2366", "4587", "1", "44",
     * "996", "0", As these aren't ThreeOdd numbers this method should
     * return 3, 12, 1, 0, 18, 0, respectively.
     *
     * @param number A string.
     * @return The sum of the even-valued digits if the string is a ThreeOdd
     * number, the sum of the odd-valued digits if the string represents a
     * number that is not a ThreeOdd number, * -1 in any other case.
     */
    public static int threeOdd(String number) {
        //FIXME: implement this method


        if (number == null || number.length() == 0) {
            return -1;
        }
        if (number.charAt(0) == '-') {
            return -1;
        }
        try {
            Integer.parseInt(number);
        } catch (Exception e) {
            return -1;
        }

        int odd = 0;
        int even = 0;
        for (int i = 0; i < number.length(); i++) {
            String[] a = number.split("");
            int digit = Integer.parseInt(a[i]);
            if (digit % 2 != 0) {
                odd += digit;
            } else {
                even += digit;
            }
        }

        if (!isThreeOdd(number)) {
            return odd;
        }
        return even;


    }

    static boolean isThreeOdd(String number) {
        if (number == null || number.length() == 0) {
            return false;
        }
        if (number.charAt(0) == '-') {
            return false;
        }
        try {
            Integer.parseInt(number);
        } catch (Exception e) {
            return false;
        }
        int i = Integer.parseInt(number);
        if (i % 3 != 0) {
            return false;
        }

        if (number.length() > 2) {
            return isThreeOdd(number.substring(1, number.length() - 1));
        }

        return true;
    }
}