Just prior to Dreamforce 2014, I launched Code Your Way In allowing developers to complete an Apex algorithm challenge for free entrance to our Topcoder Open developer conference. Feel free to try it out.

In a nutshell, the node app uses the nforce-tooling plugin for nforce I wrote to submit the code you write for the algorithm to a DE org using the Force.com Tooling API. It compiles your code and runs the accompanying unit tests that I've already written and returns the results.