php简单实现无限分类树形列表的方法

$items = array( 
  1 => array(id => 1, pid => 0, name => 江西省), 
  2 => array(id => 2, pid => 0, name => 黑龙江省),
  3 => array(id => 3, pid => 1, name => 南昌市), 
  4 => array(id => 4, pid => 2, name => 哈尔滨市),
  5 => array(id => 5, pid => 2, name => 鸡西市), 
  6 => array(id => 6, pid => 4, name => 香坊区), 
  7 => array(id => 7, pid => 4, name => 南岗区), 
  8 => array(id => 8, pid => 6, name => 和兴路), 
  9 => array(id => 9, pid => 7, name => 西大直街), 
  10 => array(id => 10, pid => 8, name => 东北林业大学),
  11 => array(id => 11, pid => 9, name => 哈尔滨工业大学),
  12 => array(id => 12, pid => 8, name => 哈尔滨师范大学),
  13 => array(id => 13, pid => 1, name => 赣州市), 
  14 => array(id => 14, pid => 13, name => 赣县), 
  15 => array(id => 15, pid => 13, name => 于都县), 
  16 => array(id => 16, pid => 14, name => 茅店镇), 
  17 => array(id => 17, pid => 14, name => 大田乡), 
  18 => array(id => 18, pid => 16, name => 义源村), 
  19 => array(id => 19, pid => 16, name => 上坝村), 
  20 => array(id => 20, pid => 0, name => 广东省), 
  21 => array(id => 21, pid => 20, name => 广州市),
); 
$t = array(); 
foreach ($items as $id => $item) { 
  if ($item[pid]) { 
    $items[$item[pid]][$item[id]] = &$items[$item[id]];
    $t[] = $id; 
  } 
} 
foreach($t as $u) { 
  unset($items[$u]); 
} 
echo "<pre>"; 
print_r($items);