MajorityElement.java

public class MajorityElement {

    public static void main(String[] args) {
        System.out.println(findMajority(new int[]{3, 4, 5, 3, 5, 3, 3, 3, 3, 5, 5, 5, 5, 5, 5, 5, 5}));
    }

    public static int findMajority(int[] array) {
        int candidate = findCandidate(array);
        return validate(array, candidate) ? candidate : -1;
    }

    private static int findCandidate(int[] array) {
        if (array == null) return -1;

        int counter = 0;
        int candidate = 0;

        for (int number : array) {
            if (counter == 0) {
                candidate = number;
            }

            if (candidate == number) {
                ++counter;
            } else {
                --counter;
            }
        }

        return candidate;
    }

    private static boolean validate(int[] array, int candidate) {
        int counter = 0;
        for (int number : array) {
            if (number == candidate) {
                counter++;
            }
        }
        return counter > array.length / 2;
    }

}