Assign classes to the right room

[lspin01l]

I'm trying to assign classes to certain rooms. I have written code that allows me to assign classes to the right room, but the trouble comes when there are not equal numbers of rooms/class types.

Here is how it is set up:
Class types: A,B,C,D
Room Types: A,B,C,D

There can only be one class of A,B,C, and the rest are D. (but it doesn't always have one of each. Sometimes one or two of the types are not there.)

There is one of each room type A,B,C and multiples of D. (this is always the case)

Im trying to figure out the logic how to assign classes to the right room type

Example.

Classes Rooms
C A
D B
D C
D D
D D
D D
D D
D D
D D


D classes can go anywhere, but A,B,C classes must go into the right A,B,C room. If an A,B,C room is not used, then a D class can go in there.

Ideas?
I don't necessarily need the VBA code for it to happen, I am just stuck on the logic behind the problem. However, if someone does post code, I'm sure its more efficient than what I could come up with.