無限級分類之查找子孫樹

<meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
<?php
function subtree($arr,$id=0,$lev=1){
	static $subs=array();
	foreach($arr as $v){
		if($v['parent']==$id){
			$v['lev']=$lev;
			$subs[]=$v;
			subtree($arr,$v['id'],$lev+1);
		}
	}
	return $subs;
}


$arr=array(
	array('id'=>1,'name'=>'安徽','parent'=>0),
	array('id'=>2,'name'=>'海淀','parent'=>7),
	array('id'=>3,'name'=>'溪縣','parent'=>5),
	array('id'=>4,'name'=>'昌平','parent'=>7),
	array('id'=>5,'name'=>'淮北','parent'=>1),
	array('id'=>6,'name'=>'朝陽','parent'=>7),
	array('id'=>7,'name'=>'北京','parent'=>0),
	array('id'=>8,'name'=>'上地','parent'=>2),
	);

 $tree=subtree($arr,0);
 foreach($tree as $v){
 	echo str_repeat('      ', $v['lev']).$v['name'].'<br/>';
 }