A bit off-topic...<p>The best online programming puzzles were the ones ITA Software posted to entice people to apply for jobs there.<p>What was effective about them was that, reading the problem, you wanted to know what a solution would look like, and knew the only way to know was to solve it. Having solved it, you wanted to know how your solution compared to others'. The only way to find out was to send it in. Having sent it, you might get an invitation to visit, and then how could you not?<p>After Google bought ITA, the puzzles were up for a while longer, then seemed to vanish. If they are archived somewhere, I would like to know where.
OT but still vaguely regarding puzzles - Jane Street has a pretty satisfying puzzle every month:<p><a href="https://www.janestreet.com/puzzles/" rel="nofollow">https://www.janestreet.com/puzzles/</a>
> Based on a small user study, we find puzzle difficulty
to correlate between human programmers and the baseline AI solvers.<p>Now that we have AI to solve "LC type of questions", can we stop asking candidates to invert a linked list in an interview.