yeah no you have to implement your own

That's ok

what about it? it's out of spec.

close this issue, we'll see later how to handle this

You don't need to list all possibilities. You need to implement a verification method to check on the fly whether the user solution is correct.

Please, respond to the message above. I really don't want to close this issue, but that is the only thing that I can do, because there is no way of implementing distribution tests into example test cases without putting testing code right there or in preloaded code. As I already said, it will be very hard and unnecesary to list all the possible solutions.

the indexing of the packages starts at 1, not at 0

Please use normal 0-based indexing. Why waste a perfectly good number? Just to try and frustrate your solvers? It adds nothing to the task, and it does detract.

let's name the drivers Jake and Alan accordingly

let's name them Jake and Elwood

apparently they've fallen on hard times :P

Hmmm.. usage of head here irks me.

sort mutates source.

So to avoid side effects, it must be copied before use.

It's good coding practice to restrict mutability. As the instance variables are never changed we can make them immutable. Even better: Thus the whole class Dinglemouse becomes immutable - an instance of Dinglemouse can never be changed after initialization. As for the parameters it might not be mandatory to declare them final, but I made it a habit to declare all variables final by default, unless for the rare occasion where I really need a mutable variable. Also it is best avoided to change the value of parameters, so declaring them final makes this more explicit.

Excuse me. why use final in this case?

what about ['b' .. 'z']?