Poundstone (awesome name) is a accessible writer, and this book is full of awesome advice for both interviewers and interviewees. If you're either hiring or applying for a job at a startup - or even anywhere in software industry - this book is an a must-read. If not, it's still a treat. It's chock-full full of awesome puzzle solving advice, and presents a number of rather clever puzzles. The advice given here - on interviewing and critical thinking - is concrete and actionable. While some sections feel a bit out of place, on the whole, this book accessible and fun.
Brief History of IQ Testing
"How Would You Move Mt Fuji" starts off by giving you a history of the "logic puzzle as an interview technique." This is probably the least relevant portion of the book. Poundstone traces the history of IQ testing, and discusses the various guises under which "intelligence tests" have been used as a "hiring filter" - for better or for worse. While it's all pretty interesting, it feels a bit out of place. The meat of the book is about logic puzzles, interviews, and their intersection, so feel free to skip the entire second chapter.
Advice for the Interviewer: Obtain Useful Information
Poundstone offers traditional interviewers the following challenge: "Is there any concievable answer to a traditional interview question that would cause you to want to hire someone on that answer alone? ... to not want to hire someone?" And if not, why is the point of the question?
This is especially important since, as Poundstone emphasizes, your final assessment of an interviewee correlates very strongly with your first impression (there are a number of convincing studies concluding as much). Thus, vague questions only make it easier to confirm your initial snap judgement. This advice is applicable to all interviews - not just "puzzle interviews." The important lesson here is: try to obtain information you can use. Does the question tell you something that helps you make a hiring decision? If not, it's probably not a good question.
Puzzle Interviews Are a Filter to Prevent Bad Hires
Puzzle interviews are a way of making sure you don't hire the wrong people. Poundstone states that a good interview puzzle should be easy enough that you're willing to reject someone who doesn't solve it. Let's take Poundstone at this word, and assume that puzzle questions are a good way of filtering bad people. Why is this useful? Simply because a false positive is much worse then a false negative. It's much more damaging to hire a bad employee than it is to pass up a good one. For this reason, ask questions where you're willing to reject someone who doesn't solve it.
When not to Ask Puzzles In an Interview
Poundstone emphasizes that puzzles are only a useful interview tool in professions where the required skillset changes fast. Programming is one such profession. For instance, let's say you hire a programmer because he's a Java wizard. This is all well and good, but this skill might become obsolete no more than two month later, when you need him to start coding in Python. A puzzle question is a good way to gauge someone's ability to engage in critical thinking in a domain-independent way.
Similarly, puzzle interviews are useful at a startup, where responsibilities a constantly shifting and uncertainty rules. Last week, you thought your startup was working on building the next great gardening app; since then, you've discovered there's not much money in the gardening app market. However, in the process of trying to build your app, you learned that HomeDepo is willing to pay you big bucks to make an app for their inventory system. Your entire business plan has changed more of less overnight. A startup employee needs to be able to push forwards in the face of striking uncertainty, and puzzle questions are one way of gauging a candidates ability identify essential elements in a situation that is fundamentally ill defined.
Importantly, this means you shouldn't use puzzles in interviews for a profession where particular stills are what matter - accountant, wedding planner, surgeon, etc.
Advice for the Interviewee: ask yourself - should this be a Monologue or Dialogue?
The first thing an interviewee should ask themselves when asked a "puzzle-like" question is: does this question anticipate a monologue or a dialog? For a legitimate "puzzle" question, you're generally expected to provide a monologue. In this case, you've been given all the info you need, and anything missing is part of the puzzle. You're expected to provide and answer in light of this missing information.
On the other hand, if you're given vague instructions, you're likely be expected to engage in a dialogue. Here, you want to ask good questions. For instance, let's say the interviewer asks, "how would you design a toaster?" This is not a puzzle question, and if you delve straight into an answer, you have failed. Instead, ask questions like, "who am I designing this for? What are my budget constraints?" and so forth.
Advice for the Interviewee: How to Tackle Puzzle Questions
When faced with a "puzzle question," many people don't know where to begin. Poundstone gives some awesome advice here: start off by explaining why the "obvious" solution is wrong - because the obvious solution almost always is wrong. In the process of figuring out why, you just might arrive at the correct answer.
Oftentimes, preliminary thinking leads to proofs of impossibility. This is a good place to look for assumptions to loosen. You'll almost never be asked an impossible question, so start questioning your assumptions - one of them must be wrong. In general, this is the best way to proceed if you're stuck: question your assumption. List them one by one, and try removing them, in order of importance (that is, loosen the least certain assumptions first).
And you often will get stuck. For this reason, you must operate on two levels: one thread tackiling the problem, and another monitoring progress. You need to know when to step back and try another approach. Don't get stuck stubbornly wrestling a dead end.
Two Cool Puzzles
How many points are there on the globe where, by walking one mile south, one mile east, and one mile north, you will reach the place where you started? (Hint: there is at least one - where is it? In addition the obvious one, there's an infinite number of other places. These make the question tricky.)
How do you cut a rectangular cake into two equal pieces when someone has already removed a rectangular piece from it? The removed piece can be of any size or orientation. You are only allowed one straight cut. (Think outside the box on this one)