An excellent demonstration of why it's a bad puzzle--there's an obvious naive solution that most people get stuck at (the 19 minute one), and a single critical

An excellent demonstration of why it's a bad puzzle--there's an obvious naive solution that most people get stuck at (the 19 minute one), and a single critical insight that reveals the otherwise simple optimal solution. It's not testing logical reasoning ability; both solutions are "obvious", which one depending on if you know the trick. It's not testing creative problem-solving; the solution is so constrained by ridiculous limitations that there's only one "correct" answer. It's not testing skills for any sort of practical, real-life situation (I hope). The main thing that questions like this reveal is whether or not the interviewee enjoys frivolous puzzles and riddles. Not the worst thing to select candidates based on I suppose, but probably not ideal, either...