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The Hardest Interview Puzzle Question Ever

Started by Mark Sands, 2009-03-20T02:53:24-05:00 (Friday)

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Mark Sands

I came across this interview question just now and think it's quite ridiculous. It's almost a combination of several rather difficult interview questions I've heard before, or so it seams like it to me. I'll post the question, and if you have an answer, go ahead and admit to it but don't post anything for a good while to give people a chance if they really want to spend the time figuring it out..unless you already know the answer. I'm very curious myself as to what it is. Good luck!

A hundred prisoners are each locked in a room with three pirates, one of whom will walk the plank in the morning. Each prisoner has 10 bottles of wine, one of which has been poisoned; and each pirate has 12 coins, one of which is counterfeit and weighs either more or less than a genuine coin. In the room is a single switch, which the prisoner may either leave as it is, or flip. Before being led into the rooms, the prisoners are all made to wear either a red hat or a blue hat; they can see all the other prisoners' hats, but not their own. Meanwhile, a six-digit prime number of monkeys multiply until their digits reverse, then all have to get across a river using a canoe that can hold at most two monkeys at a time. But half the monkeys always lie and the other half always tell the truth. Given that the Nth prisoner knows that one of the monkeys doesn't know that a pirate doesn't know the product of two numbers between 1 and 100 without knowing that the N+1th prisoner has flipped the switch in his room or not after having determined which bottle of wine was poisoned and what color his hat is, what is the solution to this puzzle?
Mark Sands
Computer Science Major

Bryan

If someone asked me that during an interview I would probably say something like "don't you have more important things to worry about?"
Bryan Grubaugh
Quickly aging alumni with too much time on his hands
Business Systems Analyst, Scripps Networks.

William Grim

Well, right now I'm wondering what exactly is the question?  I hope asking the question of what's the question isn't the answer.  If it is, sorry.
William Grim
IT Associate, Morgan Stanley

raptor

I've heard this problem before.  Don't remember the answer.
President of CAOS
Software Engineer NASA Nspires/Roses Grant

William Grim

I think three monkeys are the key to this answer.  They possess a lot of valuable knowledge and can be used to tell which monkeys are truthful or not.  Once you have determined whether a monkey is completely truthful or not, the problem gets a lot easier (not that I've fully solved it yet).  You just need to know which questions to ask the monkeys to spot the liars from the truth-tellers.
William Grim
IT Associate, Morgan Stanley

William Grim

Having said all that, I still don't know exactly the question I'm trying to answer.  However, after knowing which monkeys are honest or not, I will know which bottles are poison, which coins are counterfeit, etc.... I just don't know what should be answered.
William Grim
IT Associate, Morgan Stanley

Bryan

Having actually read the entire thing, I'm with Grim.  Is this one of those "you can't know the answer until you fully know the question" gimmicks?
Bryan Grubaugh
Quickly aging alumni with too much time on his hands
Business Systems Analyst, Scripps Networks.

Tony

This is the easiest interview question ever.  There is no answer because there is no puzzle.  It is just a bunch of facts.
I would rather be hated for doing what I believe in, than loved for doing what I don't.

William Grim

I think it depends on what they mean by "solution to the puzzle".  That's why you've got to ask them more questions.  I have a feeling it's a question to see if you pay attention to detail and know how to ask questions.
William Grim
IT Associate, Morgan Stanley


Tony

What kills me about these questions is that yeah, you might find out if the guy is good at puzzles or what not, but it doesn't really tell you what type of worker they are.  I know some pretty smart people, and some people who are good at puzzles who are horrible workers.  They are lazy, do their own thing, and aren't team players.

I have always said, when the day come that I get to ask some interview questions, I am going to ask the about a series of languages to find one they have not worked with before, and have a few ideas they may not have worked with before and I will ask them to come up with a solution to a problem involving that.  I just want to see how long it takes them to ask me or someone in the room for help, how they interact with us after they ask for help and how fast they learn. 

We don't know everything, and school isn't supposed to teach us everything.  I don't want Mr. Know-it-all, I want someone willing to learn and capable of learning quickly.
I would rather be hated for doing what I believe in, than loved for doing what I don't.

Methossa

Here's a good read (like everything else on Coding Horror) about the format of the question and the reasoning behind it. http://www.codinghorror.com/blog/archives/001243.html

One of the posts he links has this solved example near the end.

"These calculations are typically represented in the form of Fermi Questions; the canonical Fermi Question is How many piano tuners are there in Chicago?


From the almanac, we know that Chicago has a population of about 3 million people.
Assume that an average family contains four members. The number of families in Chicago is about 750,000.
If one in five families owns a piano, there will be 150,000 pianos in Chicago.
If the average piano tuner serviced four pianos every day of the week for five days, rested on weekends, and had a two week vacation during the summer, then in one year (52 weeks) he would service 1,000 pianos.
150,000 / (4 x 5 x 50) = 150
there are ~150 piano tuners in Chicago
Fermi questions are interesting, because the actual answer to the question is secondary to the process of how you arrived at the answer. Did you guess? Or did you estimate? "

William Grim

#12
Well, the "hardest question" above could be made a Fermi question with a slight twist on the question asked.  However, I don't see anything indicating the inquirer wanting an estimation of anything; the question asked as it is is too vague.

That said, I did like your link.  I think communication is extremely important, and I've turned down hiring people because they couldn't communicate their reasoning with me effectively, amongst other things.

I also like Fermi questions in general, because they open up a question to more of a problem-solving conversation.
William Grim
IT Associate, Morgan Stanley