How to Ace the Brain Teaser Interview

253 Pages·2016·21.65 MB·English

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JOHN KADOR
Author of 201 Best Questions to Ask on Your Interview
HOW TO ACE THE
BRAINTEASER
INTERVIEW
JOHN KADOR
McGraw-Hill
NEWYORK CHICAGO SAN FRANCISCO LISBON LONDON
MADRID MEXICO CITY MILAN NEW DELHI SAN JUAN
SEOUL SINGAPORE SYDNEY TORONTO
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Copyright©2005byJohnKador.Allrightsreserved.PrintedintheUnitedStatesofAmerica.
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ToPeter and Robert, mybrothers
CONTENTS
Preface v
Acknowledgments ix
To theReader xi
Chapter1 RiddleMeThis 1
Chapter2 StrategiesforSolutions 7
Chapter3 Real-WorldReasoningPuzzles 13
Puzzles 1^2
Chapter4 ReasoningPuzzles ThatDon'tRequireMath 53
Puzzles43-74
Chapter5 ReasoningPuzzlesThatRequireMath 91
Puzzles75-100
Chapter6 ProbabilityPuzzles 123
Puzzles 101-111
Chapter7 PuzzlesforProgrammersandCoders 139
Puzzles 112-119
Chapter8 BusinessCases 153
Puzzles 120-127
CONTENTS
Chapter9 GrossOrderofEstimationProblems 181
Puzzles 128-141
Chapter10 PerformancePuzzles 197
Puzzles 142-152
AppendixA: FactsYou ShouldKnow 211
AppendixB: 20Think-on-Your-FeetQuestions 213
AppendixC: AdditionalFermiProblems 215
AppendixD: PuzzlesInappropriateforJobInterviews 219
AppendixE: AdditionalSourcesandLinks 225
ListofProblems 235
PREFACE
Here's abrainteaserfor you.
Whydoemployers subjectalreadynervousjobcandidates tobrain-
teasers, puzzles, businesscases,andothermind-benders?Do such
puzzlesreallyhelpemployers buildteamsofhighlylogical,curious,
successful,hard-working, motivatedcontributorswhocanbe expected
to hit the groundrunning?
Hardlyanyonebelievesthat.Thereareno studiesthat givescientific
support to the notion that success at brainteasers and logic puzzles
predicts success at thejob. Soifemployersknowthat, why do inter
viewerspersistinusingvaluablejobinterviewtimeforthispeculiarstyle
ofinterviewing?
Interviewers look to brainteasersto do one thing: to starta safe con
versationthatreveals how smartcandidates are. Intelligence is seenas
a criticalpredictorofsuccess onthejob, and brainteasers allow inter
viewerstogetameasureofacandidate'sintelligence."There isastrong
correlation between basic intelligence and success in software engi
neering," says Ole Eichorn, chieftechnical officer (CTO) ofAperio
TechnologiesinVista,California."Unfortunatelytheforcesofpolitical
correctness havetaken awayakeytool—employers can'tgive intelli
genceteststocandidates. Inthemeantime, puzzlesareadecentproxy.
By givingcandidates goodpuzzlesyougetafairestimate ofhowsmart
theyare,andthediscussiongivesyousomeinteractionwith the candi
date, too."
Withthedownturninthetechsectors,moreandmorepeople arechas
ingfewerjobs.Interviewersareoftenfacedwithhundredsofresumes
foroneposition.Whenallthesecandidatesseemexceptionallyqualified
PREFACE
forthejob,howistheinterviewertoselect?Usingbrainteasersandpuzzles
makessenseatcompaniesthatfocusrecruitmenteffortsmore onwhat
candidatesmightdointhefuturethanonwhattheyhavedoneinthepast.
These companies understandthatintoday's fast-paced global business
world, specific skills are oflimiteduse becausetechnology changes so
quickly. Whatisreallyneeded, interviewersbelieve, arecurious, obser
vant,quick-wittedcandidateswhowelcomenewchallenges,demonstrate
mentalagilityunderstressful conditions, learnquickly, defendtheir
thinking, anddemonstrate enthusiasmforimpossibletasks.
Italsodoesn'thurtthatMicrosoft,themostsuccessfulcompanyofall
time,isknowntoaddbrainteaserstothemixofinterviewquestionsit
asksthethousandsofsuper-brightcandidateswhocomeknockingat
itsgates. Nohumanresources directorhaseverbeenfiredforaligning
hisorhercompany'shiringpracticeswithMicrosoft's.
PUZZLES AND BRAINTEASERS IN ACTION
Joel Spolsky,presidentofNewYork-basedFogCreekSoftware,under
standsthatbrainteasersorotherchallengesareacriticalpartoftheinter
viewprocessbecausetheyhelpnarrowthelargenumberof"maybes"that
crowd anyjob search. "There are three types ofpeople in the software
field," notes Spolsky,who got his firstjob atMicrosoft. "At one end of
the scale, there are the unwashedmasses, lacking even the mostbasic
skillsforthejob."Theyareeasytoferretoutandeliminate,oftenjustby
reviewingaresumeandaskingtwoorthreequickquestions.Attheother
extreme are the superstars who write compilers for fun. "And in the
middle,youhavealargenumberof'maybes' whoseemliketheymight
just be abletocontribute something,"Spolskyadds.
At FogCreek, brainteasers are used to identify candidates who not
only are smart, but who get things done. "Ourgoal is to hire people
with aptitude,not aparticularskillset,"Spolskysays."Smartisimpor
tant, buthardto define; gets thingsdoneis crucial. In orderto be able
totell,you'regoingtohavetoasktherightquestions."
Thebrainteaserchallenge comes afterSpolskyestablishes rapport
withthecandidate,asksaboutskillsandprojects,andposessomebe
havioral questions ("Tellme aboutatimewhenyou faced a deadline
crunch...").ThefirstthingSpolksylooksforinacandidateispassion.
VI
PREFACE
Afterthat, he givesthe candidate animpossible gross-orderestimation
question. "Theideaistoaskaquestionthattheyhavenopossiblewayof
answering,justtoseehowtheyhandleit,"hesays.Howmanyoptometrists
arethereinSeattle?HowmanytonsdoestheWashington Monument
weigh?HowmanygasstationsareinLosAngeles?Moreofthesepuzzles
can be foundin Chapter9.
"Whatanapplicantknowsgetshimorherthroughthefirstinterview,"
saysEdMilano,vicepresidentofMarketingandProgramDevelopment
atDesignContinuum, aproductdesignconsulting firm withoffices in
Boston,Milan, andSeoul. BythetimetheapplicantgetstoMilano, apti
tudeandexperiencearenotinquestion. ForMilanotomakeajoboffer,
hehastoseehowtheapplicant thinksunderstressfulconditions,the
environmentthatoftendescribeslifeataconsultancythatassistsclients
with make-or-breakstrategic design programs.
EdMilano,likemanyrecruiters,hasoftenfoundthatstartinganinter
viewwithabrainteaseriseffective. Logicpuzzleshavealongtradition
infast-moving high-techcompanies wherebeingquickonyourfeetis
anasset.Astherestoftheworldhasembracedtheattributesofthefast-
moving,ever-wired,start-upmentalityofthehigh-techcomputercompany,
manyrecruiters are adoptingthe in-your-facestyle ofinterviewing
associatedwithtechnology-intensivestart-ups. Somerecruitersearnestly
believe that brainteasers are valid tools to gauge the creativity, intelli
gence,passion,resourcefulness, etc.,ofcandidates. Othersarewilling
toacceptthatpuzzlesarelittlemorethaninterviewstuntsthatmayor
maynotrevealaspectsofthecandidate's characterandmayactually
alienate somecandidates.Inanycase,brainteasers arehere to stay.
Areasonable questionreaders oftenaskmeis,"Giventhatthisbook
hasnowpublishedthesebrainteasersandtheirsolutions,whywouldany
interviewerever use these brainteasers again?"
Letmegivetwoanswers. First, interviewers love candidates who
havepreparedfor interviews. Theywantyouto prepare.The fact is,
there are literally hundreds of Websites that discuss these puzzles,
sometimes with solutions, sometimesnot.Besides, many ofthese brain
teasers don'thave solutions.And ofthepuzzles that do, interviewers
understand, asyou should, thatreadingthesolutionstothesepuzzles is
no substitute for understanding them and being able to carry on an
PREFACE
intelligent conversation. And intelligent conversation—what these
brainteasersaredesignedtocatalyze—can'tbefaked.
Second, there are dozens ofinterviewingbooksthatprep candidates
onsuchstaplesofthejobinterviewas"Wheredoyouwanttobeinfive
years?"and"What'syourgreatestweakness?"butinterviewersstillask
thosequestions.Youcanbuythisbookwithconfidence.Thenextjobin
terviewbrainteaseryouareaskedislikelytobediscussedwithinthese
pages.
Goodluckonacingthebrainteaserjobinterview.
JohnKador
Geneva, Illinois
VIM
ACKNOWLEDGMENTS
Mygratitudegoes,first, tothosewhoadvisedmenottowritethisbook.
Someverysmartpeoplearguedthatitisneithervalidnormoraltomake
brainteasersapartofthejobselectionprocess,butinmakingtheircase
they contributedsome veryjuicybrainteasers thatmade theirway into
this book. Whetherwelike it ornot,job interview brainteasers are out
thereandweshouldbeprepared.AsTrotskysaid,"Youdon'thaveto
believe in street carsto takethem where youwant to go."
Dozens ofotherveterans ofthe brainteaser wars, not all ofwhom
wanttobenamedhere,helpedmecompilethesepuzzlesandtheirsolu
tions. The brainteasers themselves were offeredwith generosity. The
preferredsolutions wereheldin greaterconfidence, and I ammost
grateful to those whooccasionally bent a companypolicy or twoto
sharetheir insightswithme.Ialsoacknowledge theworkerswhore
counted their often exasperatingexperienceswithbrainteasers inthe
context oftension-filledjob interviews. Whether they operate on one
sideoftheinterviewingtable ortheother, Iamgratefultothefollowing
individualswhopermittedmetomentiontheirnames: PeterAlkemade,
AdamBarr,PhilBrady,DaleFedderson,Robert Gately,TomGentry,
VikasHamine,CharlesHandler,PeteHerzog,BenKovler,CarlKutsmode,
Marie Lerch, SteveLevy,JoeMabel,Bill McCabe,Ed Milano, Scott
Schoenick, Kevin Stone, KoenVanTolhuyzen, KevinWheeler, Jeffrey
Yamaguchi.
Scores ofWeblogs (blogs) focus on thejob interview process at
Microsoftandotherhigh-techcompanies.Anumberofbloggershelped
medefinethisbookandinvitedtheirreaderstocontributepuzzlesandper
sonalexperiences.Thisbookisricherfortheirefforts. Iwouldespecially