Multiple instances of php array recursive method

php数组递归方法

有如下php数组：

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