Magento - 我需要按字母顺序自动列出左侧导航

I need to automatically list the left nav alphabetically.

I have this code, but the problem is it only does it for category number 4 and I need it to do it for the current category. Any ideas how to get it to load the current category and not a specific number?

<?php
$cats = Mage::getModel('catalog/category')->load(4)->getChildren();
$catIds = explode(',',$cats);

$categories = array();
foreach($catIds as $catId) {
 $category = Mage::getModel('catalog/category')->load($catId); 
 $categories[$category->getName()] = $category->getUrl();
}

ksort($categories, SORT_STRING);
?>

<ul>
<?php foreach($categories as $name => $url): ?>
 <li>
 <a href="<?php echo $url; ?>"><?php echo $name; ?></a>
 </li>
<?php endforeach; ?>
</ul>

Many thanks,

Kirsty

<?php
if(Mage::registry('current_category')) {
    $cats   = Mage::registry('current_category')->getChildren();
    $catIds = explode(',',$cats);

    $categories = array();
    foreach($catIds as $catId) {
        $category = Mage::getModel('catalog/category')->load($catId);
        $categories[$category->getName()] = $category->getUrl();
    }
    ksort($categories, SORT_STRING);
    ?>
    <ul>
        <?php foreach($categories as $name => $url): ?>
            <li>
                <a href="<?php echo $url; ?>"><?php echo $name; ?></a>
            </li>
        <?php endforeach; ?>
    </ul>
<?php } ?>

For getting current category used below code -'Mage::registry('current_category')->getId()'

if(Mage::registry('current_category'))
{
$cat=Mage::registry('current_category')->getId();
/* used for category level*/
}
else{
$cat=2; // 2 is root category id
/* used for serch level*/
}
$cats = Mage::getModel('catalog/category')->load($cat)->getChildren();