Conditional offset of posts

OK, HTML and CSS I have no problem with. PHP I’m still learning. This is the situation: I have two categories, A and B. On my main page, I have a slot for the newest post (in either category). Under that, I have two columns, one with the newest 5 posts from category A, one with the newest 5 posts from category B.

What I would like to do is conditionally offset the posts in the columns so that the newest post is not displayed twice. IE, if the newest post is from category A, the category A column offsets 1 post but the category B column does not, and vice versa.

I say conditionally offset just to clarify what I’m talking about, not trying to imply this is the right technical term… I’m open to different forms of solutions. Thanks so much in advance!