PHP查找所有下级用户

/1.用户数据结构
$users = array(
    array('id'=>1, 'pid'=>0),
    array('id'=>2, 'pid'=>1),
    array('id'=>3, 'pid'=>1),
    array('id'=>4, 'pid'=>8),
    array('id'=>5, 'pid'=>3),
    array('id'=>6, 'pid'=>3),
    array('id'=>7, 'pid'=>3),
    array('id'=>8, 'pid'=>8)
); 

2. 获取团队所有下级用户
 /**
     * 获取团队所有下级用户
     * @param $users
     * @param $mid
     * @return array[id, pid]
     */
    public static function getTeamUser($mid, $users)
    {
        $teams = array();
        $mids = array($mid);

        do {
            $othermids = array();
            $state = false;
            foreach ($mids as $valueone) {
                foreach ($users as $key => $valuetwo) {
                    if ($valuetwo['pid'] == $valueone) {
                        $teams[] = $valuetwo['id'];  //找到我的下级立即添加到最终结果中
                        $othermids[] = $valuetwo['id'];  //将我的下级id保存起来用来下轮循环他的下级
                        array_splice($users, $key, 1);  //删除这个用户
                        $state = true;
                    }
                }
            }
            $mids = $othermids;  //foreach中找到的我的下级集合,用来下次循环
        } while ($state == true);
        return $teams;
    }

3. 一维数组转为字符串
  /**
     * 一维数组转为字符串
     * @param $arr
     * @return string
     */
    public static function convertArrayToString($arr)
    {
        if (!empty($arr)) {
            $strings = '';
            foreach ($arr as $item) {
                $s = (string)$item;
                $strings .= $s . ',';
            }
            $string = rtrim($strings, ',');  //删除数组最后一个字符
            return $string;
        }
        return null;
    }

4.
if ($usersSubId) {array_push($team, $usersSubId);};