Categories with only one post

My Gallery child theme has a dropdown categories menu which I like. When a category (or sub-category) is clicked, all the thumbs of posts within that category are displayed. However, when a category with only one post is clicked, it too is displayed as a thumb. I’m attempting to re-code the category template so that a page with only one post defaults to the single post template. I’m unfamiliar with what function would “count” the # of posts within that category. Something like this in the categories template?:

<?php $cat=get_post($count);
if (1==$cat)
<!– doing something with just one post –>
else
<!– default template with multiple posts –>