Restrict roles to post only in specific categories

I am having a multi-user, multi-role blogging site. I allow users to post articles on different topics. Every article has to be either of the four categories that I have – say category A, B, C, or D. All articles posted must have either of the above given categories and should fall only under one of the given categories.

I have users under two roles – Contributors and Authors. I need all my contributors to post their articles under the category of A or B only, while my default category of Contributors is A. All my authors should post articles under the category C or D only, while my default category of Authors is C.

How can I achieve this task? Can I use a plugin to achieve this or should I code it?