WP Duplicate Content Questions

Hi,

When I post to two different categories the post is available from 2 URL’s with the same content:

url.com/cat1/post-name
url.com/cat2/post-name

This could cause a problem with Search Engine duplicate content. Or does WP only ever output links to the one category so the second version should never get picked up (although it is manually acessible via typing in the URL)?

Same goes for my category pages they are accessible via:
url.com/catname
url.com/category/catname

Is this normal? Ideally i’d like to ditch the /category/ part but i’m getting the URL from a function like:

<?php
$cat = get_the_category();
$caturl = get_category_link($cat[0]->cat_ID);
echo $caturl;
?>

Would:

<?php
$cat = get_the_category();
$caturl = get_category_link($cat[0]->cat_ID);
$caturl = str_replace('/category','',$caturl);
echo $caturl;
?>

Be bad practice?