@Test
    public void test8() {
        Integer a[] = {1, 2, 3, 4, 5, 4};
        Integer b = FindNUmber(a);
        System.out.println(b);
    }


    private static Integer FindNUmber(Integer[] a) {
        Map map = new HashMap();

        for (int i = 0; i < a.length; i++) {

            if (map.containsKey(a[i])) {
                continue;
            }
            map.put(a[i], a[i]);
        }
        return null;
    }