[Tabula_Rasa]

That is a really cool idea. Is there anything similar for submitting solutions to more general programming problems, like the kinds of things they ask you to in interviews with hashing/sorting/etc? I can't figure out how the assignments are "graded" as such without logging in, it's just looking for a correct output regardless of sloppy code, or what?

[toast0]

You might try TopCoder algorithm competitions? (Especially the practice rooms with previous problems). Many of the problems are kind of interesting, but everything is expected to be solved within a limited amount of time, so you won't spend a lot of time on it. (TopCoder algorithm competitions are graded on correct output, within a limited execution time)