@Test
    public void testSample1() throws Exception {
        String[] strs = {"ab", "bb", "bc"};
        Set<String> set = new HashSet<String>();
        Collections.addAll(set, strs);
        List<List<String>> list = wordLadderII.findLadders("aa", "bc", set);
        Utils.printStringStringList(list);
    }