php怎么实现无限极分类

/** 
 * @author koma 
 * @todo   PHP无限极分类 
 */ $cn = mysql_connect('localhost', 'root', '') or die(mysql_error()); 
mysql_select_db('t', $cn) or die(mysql_error()); 
mysql_query('set names utf8'); 
 /** 
 * 从顶层逐级向下获取子类 
 * @param number $pid 
 * @param array $lists 
 * @param number $deep 
 * @return array 
 */ function getLists($pid = 0, &$lists = array(), $deep = 1) { 
    $sql = 'SELECT * FROM category WHERE pid='.$pid; 
    $res = mysql_query($sql); 
    while ( ($row = mysql_fetch_assoc($res)) !== FALSE ) { 
        $row['catename'] = str_repeat('   ', $deep).'|---'.$row['catename']; 
        $lists[] = $row; 
        getLists($row['id'], $lists, ++$deep); //进入子类之前深度+1         --$deep; 
        //从子类退出之后深度-1    
         } 
    return $lists; 
} 
 function displayLists($pid = 0, $selectid = 1) { 
    $result = getLists($pid); 
    $str = ''; 
    foreach ( $result as $item ) { 
        $selected = ""; 
        if ( $selectid == $item['id'] ) { 
            $selected = 'selected'; 
        } 
        $str .= ''.$item['catename'].''; 
    } 
    return $str .= ''; 
} /** 
 * 从子类开始逐级向上获取其父类 
 * @param number $cid 
 * @param array $category 
 * @return array: 
 */ function getCategory($cid, &$category = array()) { 
    $sql = 'SELECT * FROM category WHERE id='.$cid.' LIMIT 1'; 
    $result = mysql_query($sql); 
    $row = mysql_fetch_assoc($result); 
    if ( $row ) { 
        $category[] = $row; 
        getCategory($row['pid'], $category); 
    } 
    krsort($category); //逆序,达到从父类到子类的效果     return $category; 
} 
 function displayCategory($cid) { 
    $result = getCategory($cid); 
    $str = ""; 
    foreach ( $result as $item ) { 
        $str .= ''.$item['catename'].'>'; 
    } 
    return substr($str, 0, strlen($str) - 1); 
} 
 echo displayLists(0, 3); 
 echo displayCategory(13);