问下如何生成所有的不重复的数组

$str    = 'abc';
$res    = Arrangement( $str );
print_r($res);

function Arrangement($arr = array(), $res = '') {
  if(! is_array($arr) ) $arr = str_split($arr);
  if(empty($arr)) $array[] = $res;
  else foreach($arr AS $k => $v) {
    unset($arr[$k]);
    foreach( Arrangement($arr, $res . $v) AS $t) $array[] = $t;
    $arr[$k]    = $v;
  }
  return  $array;
}

Array
(
    [0] => abc
    [1] => acb
    [2] => bca
    [3] => bac
    [4] => cab
    [5] => cba
)