php数组递归方法

$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'), 
); 

方法一； 
function gentree5($items) { 
    foreach ($items as $item) 
        $items[$item['pid']]['son'][$item['id']] = &$items[$item['id']]; 
    return isset($items[0]['son']) ? $items[0]['son'] : array(); 
} 

方法二： 
    function findchild($arr,$id){ 
      $childs=array(); 
     foreach ($arr as $k => $v){ 
         if($v['pid']== $id){ 
              $childs[]=$v; 
         } 
    } 
//    echo "

";print_r($childs);die(); <br>    return $childs; <br>} <br><br>function build_tree($root_id){ <br>    global $items; <br>    $childs =array(); <br>    $childs=findchild($items,$root_id); <br>//    print_r($childs); <br>//    die(); <br>    if(empty($childs)){ <br>        return null; <br>    } <br>   foreach ($childs as $k => $v){ <br>       $rescurtree=build_tree($v['id']); <br>       if( null !=   $rescurtree){ <br>       $childs[$k]['son']=$rescurtree; <br>       } <br>   } <br>    return $childs; <br>}