MaxProductMultipleOfNine.java

    public static int maxProductMultipleOfNine(int[] numbers)  {

        if (numbers.length < 2) {
            return 0;
        }
        if (numbers.length == 2 && (numbers[0] * numbers[1] % 9 == 0)) {
            return numbers[0] * numbers[1];
        }

        int max9 = 0, max = 0, max3 = 0, max3_1 = 0;

        for (int i = 0; i < numbers.length; i++) {
            int candidate = numbers[i];
            if (candidate % 3 == 0) {
                if (candidate > max3) {
                    if (max3 > max3_1) {
                        max3_1 = max3;
                    }
                    max3 = candidate;
                } else if (candidate > max3_1) {
                    max3_1 = candidate;
                }
            }
            if (candidate % 9 == 0) {
                if (candidate > max9) {
                    max9 = candidate;
                }
            } else if (candidate > max) {
                max = candidate;
            }
        }

        return Math.max(max9 * max, max3 * max3_1);

    }