php简单代码实现无限分类树形列表

$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);