PHP 递归实现层级树状展现数据

<?php  
   
$db = mysql_connect('localhost', 'root', 'root') or die('Can\'t connect to database');  
mysql_select_db('test') or die('Can\'t find database : test');  
$result = mysql_query('select id, fid, name from tree');  
while($arr = mysql_fetch_array($result)){  
    $data[] = array(  
        'id' => $arr['id'],   
        'fid' => $arr['fid'],  
        'name' => $arr['name'],   
    );  
}  
   
// 将数据按照缩进简单排列 见图1  
function data2arr($tree, $rootId = 0, $level = 0) {  
    foreach($tree as $leaf) {  
        if($leaf['fid'] == $rootId) {  
            echo str_repeat('    ', $level) . $leaf['id'] . ' ' . $leaf['name'] . '<br/>';  
            foreach($tree as $l) {  
                if($l['fid'] == $leaf['id']) {  
                    data2arr($tree, $leaf['id'], $level + 1);  
                    break;  
                }  
            }  
        }  
    }  
}  
   
data2arr($data);  
echo '<br/>-----------------------------------------------------------------------<br/>';  
   
// 将数据按照所属关系封装 见图2  
function arr2tree($tree, $rootId = 0) {  
    $return = array();  
    foreach($tree as $leaf) {  
        if($leaf['fid'] == $rootId) {  
            foreach($tree as $subleaf) {  
                if($subleaf['fid'] == $leaf['id']) {  
                    $leaf['children'] = arr2tree($tree, $leaf['id']);  
                    break;  
                }  
            }  
            $return[] = $leaf;  
        }  
    }  
    return $return;  
}  
   
$tree = arr2tree($data);  
print_r($tree);  
echo '<br/>-----------------------------------------------------------------------<br/>';  
   
// 将数据使用HTML再次展现 见图3  
function tree2html($tree) {  
    echo '<ul>';  
    foreach($tree as $leaf) {  
        echo '<li>' .$leaf['name'];  
        if(! emptyempty($leaf['children'])) tree2html($leaf['children']);  
        echo '</li>';  
    }  
    echo '</ul>';  
}  
   
tree2html($tree);