Mastermind Codebreaker Challenge
mastermind.rubikloud.com
mastermind.rubikloud.com
http://en.wikipedia.org/wiki/Mastermind_%28board_game%29
tl;dr answer: Check every possible move. For each possible move, each possible response partitions the remaining guesses. Find the move that, with the worst possible response, has the fewest possible remaining guesses. That is an almost-optimal greedy algorithm.
Second, as a senior candidate I now pass on pre-interview screening tests and assignments. I'm not spending a couple hours doing your challenge for the chance of MAYBE getting an interview. A pre-interview test only works for a recent grad or someone who's desperate.
Who are you and why is your job so special, that I should invest several hours of time for the chance of maybe speaking with you?
Recent grads aside, screening is stupid and hipster edgy "only the best" companies tend to do this kind of stuff. Unless the company legitimately does cutting edge work (quant trading firm, Google, etc) there's is absolutely no need for this.
On topic though, the problem is an interesting exercise in AI. Could be fun.
People often lie on their resumes. A while ago when I was hiring, I would throw 90% of the resumes I got because they weren't what I was looking for (one way or the other), but of the 10% that were left, many were simply lies - I didn't keep stats, but phone screens weeded out most of the fakes, though some slipped through and were only weeded in person.
People who say "screening is unneeded" have never likely tried to hire, or have access to a pool of honest-resume talent that most of us do not (which I find highly unlikely).
Also, giving me a pre-screening test is insulting and shows you didn't read my resume. Based on my education, various honors, and experience, wouldn't it be at least worth your while to talk with me before making me take your stupid test?
And you shouldn't. Or at least, you should do them prioritized in the order of where you want to work.
> Based on my education, various honors, and experience, wouldn't it be at least worth your while to talk with me before making me take your stupid test?
Unfortunately, a significant percentage of resumes are inaccurate (to put it lightly; "outright lies" is a better description), so you might have equally asked "Based on the color of my eyes, wouldn't it ...."
Pre-screening is better for everyone. If you came to my office for an interview, or if I interviewed you by phone, I would do something that would (should) take comparable amount of time. Wouldn't you like to save the commute?
Personally, I try to hire by reference-from-someone-I-know rather than blindly. It is about 100 times more effective (in time spent; I don't think I'm exaggerating).