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You need to toss a coin for a football match. The only coin you have is
bent and biased towards one outcome. How do you use the coin and ensure a
fair toss?
I love a good a puzzle and there are certainty plenty
of thought provoking mind benders in this book - most of which I had
not heard before. Author
William Poundstone (author of '
How Would You Move Mount Fuji' and '
Fortune's Formula')
describes various puzzles that
are describes various puzzles that are likely to be part of a Google
interview process - that company now estimated to be running over one
billion search requests per day! Some other aspects of Google are
covered, but the subject matter is predominately puzzles - all types of
puzzles: fermi questions, deductive logic, numeracy skill, algorithmic
questions and some grade A counter intuitive mind boggling teasers!
 |
| William Poundstone |
One can't help asking the question why Google bothers with all of this?
Surely, the point of an interview is to see if someone can do a certain
type of work and the interview should be a fair attempt to assess a
candidate's suitability. I have had the fortune (some would say
misfortune) to be part of world of Software engineering for the last 15
years. I am passionate about it, but I'll be the first to admit it
isn't just about solving fun puzzles. Following best practises,
following agreed processes, keeping up to speed with technology,
documenting solutions so others can see what's going on are all very
important things to make a good software engineer. And it's not always
sexy work. Sometimes it requires patience debugging ugly code while
sticking to a tight project deadline. Ascertaining how good someone is
at all this in an interview setting can be difficult - especially when
it's very easy for a good candidate to freeze from nerves or get an
unexpected mental block. It's very difficult to objectify what makes a
good software engineer. Sometimes someone very intelligent can get hung
up on abstractions or theoritical patterns and forget they have
deadlines or just not be a good team player. Sometimes, there's just
inescapable subjectivity.
 |
| Joel Spolksy |
So how do brain teasers help out? Acclaimed tech guru, Joel Spolsky
advises to avoid asking them in interviews because they are usually just
a case of either the candidate knows it or he doesn't - and not much
else. In my opinion, it can take months to understand someone's
technical strengths and weaknesses. Puzzles can be useful for
demostrating how someone approaches problem solving, how they think on
their feet and how they communicate ideas. So yes they do serve a
purpose. But even if they serve no purpose whatsoever other than a bit
of fun, that's fine for me. I love a good puzzle so I really enjoyed
this book and for that reason I'd recommend it to anyone who likes to
dabble in some cryptic challenges.
Comments
Jean-Baptiste Nizet replied on Fri, 2012/06/01 - 9:33am
You need to toss a coin for a football match. The only coin you have is bent and biased towards one outcome. How do you use the coin and ensure a fair toss?
My take: you hide the coin in one of your hands behind your back and ask which hand holds the coin.
Am I hired?
Francis Perreault replied on Fri, 2012/06/01 - 10:58am
in response to:
Jean-Baptiste Nizet
Peter Levart replied on Sat, 2012/06/02 - 11:32am
My take:
You toss the coin multiple times until the outcome of two consecutive tosses is different. Then you take the outcome of the last toss as the deciding outcome.
Nick Maiorano replied on Sat, 2012/06/02 - 3:26pm
While these responses are certainly creative, they don't actually solve the problem of using the coin to ensure a fair outcome. The solution is very simple: you have to use odds, just like at the race track, to compensate for the fact the 2 sides of the coin don't have an equal chance in the coin toss. If, for example, heads has been determined to come out of 3 of every 4 tosses, then you must toss the coin 4 times. If 3 or more tosses result in heads, then heads wins otherwise tails is the winner. It's a boring but effective solution - just like good software ought to be.
Peter Levart replied on Wed, 2012/06/06 - 3:23pm
in response to:
Nick Maiorano
Nick,
What do you do if "for example, heads has been determined to come out 2 of every Pi tosses" ?
Nick Maiorano replied on Wed, 2012/06/06 - 8:23pm
in response to:
Peter Levart
Jaime Martin replied on Wed, 2012/08/29 - 7:45pm
Peter is correct as long as you toss the coin in pairs - otherwise you are just reversing the odds.
When thrown in pairs the probability of a head followed by tails is equal to the probability of tails followed by a head.
Nick's idea was my first thought but a football game has to be played so we have no time for the amount of trials needed to detrmine the bias.