If the user expands on their answer, then the asker gets their problem solved incredibly quickly, which is awesome.
If not, the answer is likely to be downvoted (or deleted if it's not a real answer). In past contests negatively scored posts didn't count, I would asssume that's the case here as well. If not, I think it should be!
Posting the short answer, without all the extra details a person might want to know and then expanding it in a series of intelligent edits is a very responsible thing to do.
It gives the asker a quick answer, as quickly as the answerer can, and it also gives the complete answer, as quickly as the answerer can. The poster is being maximally helpful, and is ...