public List<V> reverseTopologicalSort() {
        List<V> list = topologicalSort();
        if (list == null) {
            return null;
        }

        Collections.reverse(list);

        return list;
    }
@Test
    void reverseTopologicalSort() {
        List<Character> result = graph.reverseTopologicalSort();
        List<Character> expected = Arrays.asList('C', 'G', 'F', 'B', 'A', 'E', 'D');
        assertEquals(expected, result);
    }