a) the solution assumes you can put two cars on a turntable... can you? b) couldn't the solution have been to just manually move the TOILET sign on the toilet-less cars as appropriate?

Finally the real take-away here is that cost-cutting always has external costs that are seldom thought of, and especially when they harm the product experience, should definitely be re-evaluated :)

edit: I realize I was wrong, you don't need to ever put pairs on a turn-table as long as you keep them paired correctly.