@Test
  public void test2() {

    Set<String> res = new HashSet<String>();
    res = Permute.permutation("abc");
    String[] out = res.toArray(new String[res.size()]);
    String[] exp = {"bca", "acb", "abc", "cba", "bac", "cab"};
    assertArrayEquals(exp, out);
  }
  @Test
  public void test1() {

    Set<String> res = new HashSet<String>();
    res = Permute.permutation("111b");
    String[] out = res.toArray(new String[res.size()]);
    String[] exp = {"b111", "1b11", "111b", "11b1"};
    assertArrayEquals(exp, out);
  }