php 无限分类 树形数据 格式化

<?php 
function genTree($items,$id='id',$pid='pid',$son = 'children'){
	$tree = array(); //格式化的树
	$tmpMap = array();  //临时扁平数据
	
	foreach ($items as $item) {
		$tmpMap[$item[$id]] = $item;
	}
	
	foreach ($items as $item) {
		if (isset($tmpMap[$item[$pid]])) {
			$tmpMap[$item[$pid]][$son][] = &$tmpMap[$item[$id]];
		} else {
			$tree[] = &$tmpMap[$item[$id]];
		}
	}
	unset($tmpMap);
	return $tree;
}

$items1 = array(
        array('id' => 1, 'pid' => 0, 'name' => '一级11' ),
        array('id' => 11, 'pid' => 0, 'name' => '一级12' ),
        array('id' => 2, 'pid' => 1, 'name' => '二级21' ),
        array('id' => 10, 'pid' => 11, 'name' => '二级22' ),
        array('id' => 3, 'pid' => 1, 'name' => '二级23' ),
        array('id' => 12, 'pid' => 11, 'name' => '二级24' ),
        array('id' => 9, 'pid' => 1, 'name' => '二级25' ),
        array('id' => 14, 'pid' => 1, 'name' => '二级26' ),
        array('id' => 4, 'pid' => 9, 'name' => '三级31' ),
        array('id' => 6, 'pid' => 9, 'name' => '三级32' ),
        array('id' => 7, 'pid' => 4, 'name' => '四级41' ),
        array('id' => 8, 'pid' => 4, 'name' => '四级42' ),
        array('id' => 5, 'pid' => 4, 'name' => '四级43' ),
        array('id' => 13, 'pid' => 4, 'name' => '四级44' ),
        array('id' => 15, 'pid' => 8, 'name' => '五级51' ),
        array('id' => 16, 'pid' => 8, 'name' => '五级52' ),
        array('id' => 17, 'pid' => 8, 'name' => '五级53' ),
        array('id' => 18, 'pid' => 16, 'name' => '六级64' ),
); 

$time1 = microtime(true);
var_dump(genTree($items1));
$time2 = microtime(true);
echo "function 时间1：".($time2-$time1);
?>