PHP树不需要递归

/**
 * 创建父节点树形数组
 * 参数
 * $ar 数组，邻接列表方式组织的数据
 * $id 数组中作为主键的下标或关联键名
 * $pid 数组中作为父键的下标或关联键名
 * 返回 多维数组
 **/
function find_parent($ar, $id='id', $pid='pid') {
  foreach($ar as $v) $t[$v[$id]] = $v;
  foreach ($t as $k => $item){
    if( $item[$pid] ){
      if( ! isset($t[$item[$pid]]['parent'][$item[$pid]]) )
         $t[$item[$id]]['parent'][$item[$pid]] =& $t[$item[$pid]];
    }
  }
  return $t;
}


/**
 * 创建子节点树形数组
 * 参数
 * $ar 数组，邻接列表方式组织的数据
 * $id 数组中作为主键的下标或关联键名
 * $pid 数组中作为父键的下标或关联键名
 * 返回 多维数组
 **/
function find_child($ar, $id='id', $pid='pid') {
  foreach($ar as $v) $t[$v[$id]] = $v;
  foreach ($t as $k => $item){
    if( $item[$pid] ) {
      $t[$item[$pid]]['child'][$item[$id]] =& $t[$k];
    }
  }
  return $t;
}

    $data = array(
      array('ID'=>1, 'PARENT'=>0, 'NAME'=>'祖父'),
      array('ID'=>2, 'PARENT'=>1, 'NAME'=>'父亲'),
      array('ID'=>3, 'PARENT'=>1, 'NAME'=>'叔伯'),
      array('ID'=>4, 'PARENT'=>2, 'NAME'=>'自己'),
      array('ID'=>5, 'PARENT'=>4, 'NAME'=>'儿子'),
    );

    $p = find_parent($data, 'ID', 'PARENT');
    $c = find_child($data, 'ID', 'PARENT');
    Print_r ($c);

执行效果:

Array
(
    [1] => Array
        (
            [ID] => 1
            [PARENT] => 0
            [NAME] => 祖父
            [child] => Array
                (
                    [2] => Array
                        (
                            [ID] => 2
                            [PARENT] => 1
                            [NAME] => 父亲
                            [child] => Array
                                (
                                    [4] => Array
                                        (
                                            [ID] => 4
                                            [PARENT] => 2
                                            [NAME] => 自己
                                            [child] => Array
                                                (
                                                    [5] => Array
                                                        (
                                                            [ID] => 5
                                                            [PARENT] => 4
                                                            [NAME] => 儿子
                                                        )

                                                )

                                        )

                                )

                        )

                    [3] => Array
                        (
                            [ID] => 3
                            [PARENT] => 1
                            [NAME] => 叔伯
                        )

                )

        )

    [2] => Array
        (
            [ID] => 2
            [PARENT] => 1
            [NAME] => 父亲
            [child] => Array
                (
                    [4] => Array
                        (
                            [ID] => 4
                            [PARENT] => 2
                            [NAME] => 自己
                            [child] => Array
                                (
                                    [5] => Array
                                        (
                                            [ID] => 5
                                            [PARENT] => 4
                                            [NAME] => 儿子
                                        )

                                )

                        )

                )

        )

    [3] => Array
        (
            [ID] => 3
            [PARENT] => 1
            [NAME] => 叔伯
        )

    [4] => Array
        (
            [ID] => 4
            [PARENT] => 2
            [NAME] => 自己
            [child] => Array
                (
                    [5] => Array
                        (
                            [ID] => 5
                            [PARENT] => 4
                            [NAME] => 儿子
                        )

                )

        )

    [5] => Array
        (
            [ID] => 5
            [PARENT] => 4
            [NAME] => 儿子
        )

)