9:05
How NOT to dress up for a job fair
http://www.flickr.com/photos/16577770@N00/2329011550/sizes/m/
I've been meaning to write up some tips on interviewing at
Google for a good long time now. I keep putting it off, though,
because it's going to make you mad. Probably. For some
statistical definition of "you", it's very likely to upset you.
Why? Because... well, here, I wrote a little ditty about it:
Hey man, I don't know that stuffStevey's talking abooooooutIf my
boss thinks it's importantI'm gonna get fiiiiiiiiiiredOooh yeah
baaaby baaaay-beeeeee....
I didn't realize this was such a typical reaction back when I
first started writing about interviewing, way back at other
companies. Boy-o-howdy did I find out in a hurry.
See, it goes like this:
Me: blah blah blah, I like asking question X in interviews, blah
blah blah...
You: Question X? Oh man, I haven't heard about X since college!
I've never needed it for my job! He asks that in interviews? But
that means someone out there thinks it's important to know, and,
and... I don't know it! If they detect my ignorance, not only
will I be summarily fired for incompetence without so much as a
thank-you, I will also be unemployable by people who ask
question X! If people listen to Stevey, that will be everyone! I
will become homeless and destitute! For not knowing something
I've never needed before! This is horrible! I would attack X
itself, except that I do not want to pick up a book and figure
enough out about it to discredit it. Clearly I must yell a lot
about how stupid Stevey is so that nobody will listen to him!
Me: So in conclusion, blah blah... huh? Did you say "fired"?
"Destitute?" What are you talking about?
You: Aaaaaaauuuggh!!! *stab* *stab* *stab*
Me: That's it. I'm never talking about interviewing again.
It doesn't matter what X is, either. It's arbitrary. I could
say: "I really enjoy asking the candidate (their name) in
interviews", and people would still freak out, on account of
insecurity about either interviewing in general or their
knowledge of their own name, hopefully the former.
But THEN, time passes, and interview candidates come and go, and
we always wind up saying: "Gosh, we sure wish that obviously
smart person had prepared a little better for his or her
interviews. Is there any way we can help future candidates out
with some tips?"
And then nobody actually does anything, because we're all afraid
of getting stabbed violently by People Who Don't Know X.
I considered giving out a set of tips in which I actually use
variable names like X, rather than real subjects, but decided
that in the resultant vacuum, everyone would get upset.
Otherwise that approach seemed pretty good, as long as I
published under a pseudonym.
In the end, people really need the tips, regardless of how many
feelings get hurt along the way. So rather than skirt around the
issues, I'm going to give you a few mandatory substitutions for
X along with a fair amount of general interview-prep
information.
Caveats and Disclaimers
This blog is not endorsed by Google. Google doesn't know I'm
publishing these tips. It's just between you and me, OK? Don't
tell them I prepped you. Just go kick ass on your interviews and
we'll be square.
I'm only talking about general software engineering positions,
and interviews for those positions.
These tips are actually generic; there's nothing specific to
Google vs. any other software company. I could have been writing
these tips about my first software job 20 years ago. That
implies that these tips are also timeless, at least for the span
of our careers.
These tips obviously won't get you a job on their own. My hope
is that by following them you will perform your very best during
the interviews.
Oh, and um, why Google?
Oho! Why Google, you ask? Well let's just have that dialog right
up front, shall we?
You: Should I work at Google? Is it all they say it is, and
more? Will I be serenely happy there? Should I apply
immediately?
Me: Yes.
You: To which ques... wait, what do you mean by "Yes?" I didn't
even say who I am!
Me: Dude, the answer is Yes. (You may be a woman, but I'm still
calling you Dude.)
You: But... but... I am paralyzed by inertia! And I feel a
certain comfort level at my current company, or at least I have
become relatively inured to the discomfort. I know people here
and nobody at Google! I would have to learn Google's build
system and technology and stuff! I have no credibility, no
reputation there I would have to start over virtually from
scratch! I waited too long, there's no upside! I'm afraaaaaaid!
Me: DUDE. The answer is Yes already, OK? It's an invariant.
Everyone else who came to Google was in the exact same position
as you are, modulo a handful of famous people with beards that
put Gandalf's to shame, but they're a very tiny minority.
Everyone who applied had the same reasons for not applying as
you do. And everyone here says: "GOSH, I SURE AM HAPPY I CAME
HERE!" So just apply already. But prep first.
You: But what if I get a mistrial? I might be smart and
qualified, but for some random reason I may do poorly in the
interviews and not get an offer! That would be a huge blow to my
ego! I would rather pass up the opportunity altogether than have
a chance of failure!
Me: Yeah, that's at least partly true. Heck, I kinda didn't make
it in on my first attempt, but I begged like a street dog until
they gave me a second round of interviews. I caught them in a
weak moment. And the second time around, I prepared, and did
much better.
The thing is, Google has a well-known false negative rate, which
means we sometimes turn away qualified people, because that's
considered better than sometimes hiring unqualified people. This
is actually an industry-wide thing, but the dial gets turned
differently at different companies. At Google the false-negative
rate is pretty high. I don't know what it is, but I do know a
lot of smart, qualified people who've not made it through our
interviews. It's a ummer.
But the really important takeaway is this: if you don't get an
offer, you may still be qualified to work here. So it needn't be
a blow to your ego at all!
As far as anyone I know can tell, false negatives are completely
random, and are unrelated to your skills or qualifications. They
can happen from a variety of factors, including but not limited
to:
you're having an off day
one or more of your interviewers is having an off day
there were communication issues invisible to you and/or one or
more of the interviewers
you got unlucky and got an Interview Anti-Loop
Oh no, not the Interview Anti-Loop!
Yes, I'm afraid you have to worry about this.
What is it, you ask? Well, back when I was at Amazon, we did
(and they undoubtedly still do) a LOT of soul-searching about
this exact problem. We eventually concluded that every single
employee E at Amazon has at least one "Interview Anti-Loop": a
set of other employees S who would not hire E. The root cause is
important for you to understand when you're going into
interviews, so I'll tell you a little about what I've found over
the years.
First, you can't tell interviewers what's important. Not at any
company. Not unless they're specifically asking you for advice.
You have a very narrow window of perhaps one year after an
engineer graduates from college to inculcate them in the art of
interviewing, after which the window closes and they believe
they are a "good interviewer" and they don't need to change
their questions, their question styles, their interviewing
style, or their feedback style, ever again.
It's a problem. But I've had my hand bitten enough times that I
just don't try anymore.
Second problem: every "experienced" interviewer has a set of pet
subjects and possibly specific questions that he or she feels is
an accurate gauge of a candidate's abilities. The question sets
for any two interviewers can be widely different and even
entirely non-overlapping.
A classic example found everywhere is: Interviewer A always asks
about C++ trivia, filesystems, network protocols and discrete
math. Interviewer B always asks about Java trivia, design
patterns, unit testing, web frameworks, and software project
management. For any given candidate with both A and B on the
interview loop, A and B are likely to give very different votes.
A and B would probably not even hire each other, given a chance,
but they both happened to go through interviewer C, who asked
them both about data structures, unix utilities, and processes
versus threads, and A and B both happened to squeak by.
That's almost always what happens when you get an offer from a
tech company. You just happened to squeak by. Because of the
inherently flawed nature of the interviewing process, it's
highly likely that someone on the loop will be unimpressed with
you, even if you are Alan Turing. Especially if you're Alan
Turing, in fact, since it means you obviously don't know C++.
The bottom line is, if you go to an interview at any software
company, you should plan for the contingency that you might get
genuinely unlucky, and wind up with one or more people from your
Interview Anti-Loop on your interview loop. If this happens, you
will struggle, then be told that you were not a fit at this
time, and then you will feel bad. Just as long as you don't feel
meta-bad, everything is OK. You should feel good that you feel
bad after this happens, because hey, it means you're human.
And then you should wait 6-12 months and re-apply. That's pretty
much the best solution we (or anyone else I know of) could come
up with for the false-negative problem. We wipe the slate clean
and start over again. There are lots of people here who got in
on their second or third attempt, and they're kicking butt.
You can too.
OK, I feel better about potentially not getting hired
Good! So let's get on to those tips, then.
If you've been following along very closely, you'll have
realized that I'm interviewer D. Meaning that my personal set of
pet questions and topics is just my own, and it's no better or
worse than anyone else's. So I can't tell you what it is, no
matter how much I'd like to, because I'll offend interviewers A
through X who have slightly different working sets.
Instead, I want to prep you for some general topics that I
believe are shared by the majority of tech interviewers at
Google-like companies. Roughly speaking, this means the company
builds a lot of their own software and does a lot of distributed
computing. There are other tech-company footprints, the opposite
end of the spectrum being companies that outsource everything to
consultants and try to use as much third-party software as
possible. My tips will be useful only to the extent that the
company resembles Google.
So you might as well make it Google, eh?
First, let's talk about non-technical prep.
The Warm-Up
Nobody goes into a boxing match cold. Lesson: you should bring
your boxing gloves to the interview. No, wait, sorry, I mean:
warm up beforehand!
How do you warm up? Basically there is short-term and long-term
warming up, and you should do both.
Long-term warming up means: study and practice for a week or two
before the interview. You want your mind to be in the general
"mode" of problem solving on whiteboards. If you can do it on a
whiteboard, every other medium (laptop, shared network document,
whatever) is a cakewalk. So plan for the whiteboard.
Short-term warming up means: get lots of rest the night before,
and then do intense, fast-paced warm-ups the morning of the
interview.
The two best long-term warm-ups I know of are:
1) Study a data-structures and algorithms book. Why? Because it
is the most likely to help you beef up on problem
identification. Many interviewers are happy when you understand
the broad class of question they're asking without explanation.
For instance, if they ask you about coloring U.S. states in
different colors, you get major bonus points if you recognize it
as a graph-coloring problem, even if you don't actually remember
exactly how graph-coloring works.
And if you do remember how it works, then you can probably whip
through the answer pretty quickly. So your best bet,
interview-prep wise, is to practice the art of recognizing that
certain problem classes are best solved with certain algorithms
and data structures.
My absolute favorite for this kind of interview preparation is
Steven Skiena's The Algorithm Design Manual. More than any other
book it helped me understand just how astonishingly commonplace
(and important) graph problems are they should be part of
every working programmer's toolkit. The book also covers basic
data structures and sorting algorithms, which is a nice bonus.
But the gold mine is the second half of the book, which is a
sort of encyclopedia of 1-pagers on zillions of useful problems
and various ways to solve them, without too much detail. Almost
every 1-pager has a simple picture, making it easy to remember.
This is a great way to learn how to identify hundreds of problem
types.
Other interviewers I know recommend Introduction to Algorithms.
It's a true classic and an invaluable resource, but it will
probably take you more than 2 weeks to get through it. But if
you want to come into your interviews prepped, then consider
deferring your application until you've made your way through
that book.
2) Have a friend interview you. The friend should ask you a
random interview question, and you should go write it on the
board. You should keep going until it is complete, no matter how
tired or lazy you feel. Do this as much as you can possibly
tolerate.
I didn't do these two types of preparation before my first
Google interview, and I was absolutely shocked at how bad at
whiteboard coding I had become since I had last interviewed
seven years prior. It's hard! And I also had forgotten a bunch
of algorithms and data structures that I used to know, or at
least had heard of.
Going through these exercises for a week prepped me mightily for
my second round of Google interviews, and I did way, way better.
It made all the difference.
As for short-term preparation, all you can really do is make
sure you are as alert and warmed up as possible. Don't go in
cold. Solve a few problems and read through your study books.
Drink some coffee: it actually helps you think faster, believe
it or not. Make sure you spend at least an hour practicing
immediately before you walk into the interview. Treat it like a
sports game or a music recital, or heck, an exam: if you go in
warmed up you'll give your best performance.
Mental Prep
So! You're a hotshot programmer with a long list of
accomplishments. Time to forget about all that and focus on
interview survival.
You should go in humble, open-minded, and focused.
If you come across as arrogant, then people will question
whether they want to work with you. The best way to appear
arrogant is to question the validity of the interviewer's
question it really ticks them off, as I pointed out earlier
on. Remember how I said you can't tell an interviewer how to
interview? Well, that's especially true if you're a candidate.
So don't ask: "gosh, are algorithms really all that important?
do you ever need to do that kind of thing in real life? I've
never had to do that kind of stuff." You'll just get rejected,
so don't say that kind of thing. Treat every question as
legitimate, even if you are frustrated that you don't know the
answer.
Feel free to ask for help or hints if you're stuck. Some
interviewers take points off for that, but occasionally it will
get you past some hurdle and give you a good performance on what
would have otherwise been a horrible stony half-hour silence.
Don't say "choo choo choo" when you're "thinking".
Don't try to change the subject and answer a different question.
Don't try to divert the interviewer from asking you a question
by telling war stories. Don't try to bluff your interviewer. You
should focus on each problem they're giving you and make your
best effort to answer it fully.
Some interviewers will not ask you to write code, but they will
expect you to start writing code on the whiteboard at some point
during your answer. They will give you hints but won't
necessarily come right out and say: "I want you to write some
code on the board now." If in doubt, you should ask them if they
would like to see code.
Interviewers have vastly different expectations about code. I
personally don't care about syntax (unless you write something
that could obviously never work in any programming language, at
which point I will dive in and verify that you are not, in fact,
a circus clown and that it was an honest mistake). But some
interviewers are really picky about syntax, and some will even
silently mark you down for missing a semicolon or a curly brace,
without telling you. I think of these interviewers as well,
it's a technical term that rhymes with "bass soles", but they
think of themselves as brilliant technical evaluators, and
there's no way to tell them otherwise.
So ask. Ask if they care about syntax, and if they do, try to
get it right. Look over your code carefully from different
angles and distances. Pretend it's someone else's code and
you're tasked with finding bugs in it. You'd be amazed at what
you can miss when you're standing 2 feet from a whiteboard with
an interviewer staring at your shoulder blades.
It's OK (and highly encouraged) to ask a few clarifying
questions, and occasionally verify with the interviewer that
you're on the track they want you to be on. Some interviewers
will mark you down if you just jump up and start coding, even if
you get the code right. They'll say you didn't think carefully
first, and you're one of those "let's not do any design" type
cowboys. So even if you think you know the answer to the
problem, ask some questions and talk about the approach you'll
take a little before diving in.
On the flip side, don't take too long before actually solving
the problem, or some interviewers will give you a delay-of-game
penalty. Try to move (and write) quickly, since often
interviewers want to get through more than one question during
the interview, and if you solve the first one too slowly then
they'll be out of time. They'll mark you down because they
couldn't get a full picture of your skills. The benefit of the
doubt is rarely given in interviewing.
One last non-technical tip: bring your own whiteboard dry-erase
markers. They sell pencil-thin ones at office supply stores,
whereas most companies (including Google) tend to stock the fat
kind. The thin ones turn your whiteboard from a 480i
standard-definition tube into a 58-inch 1080p HD plasma screen.
You need all the help you can get, and free whiteboard space is
a real blessing.
You should also practice whiteboard space-management skills,
such as not starting on the right and coding down into the
lower-right corner in Teeny Unreadable Font. Your interviewer
will not be impressed. Amusingly, although it always irks me
when people do this, I did it during my interviews, too. Just be
aware of it!
Oh, and don't let the marker dry out while you're standing there
waving it. I'm tellin' ya: you want minimal distractions during
the interview, and that one is surprisingly common.
OK, that should be good for non-tech tips. On to X, for some
value of X! Don't stab me!
Tech Prep Tips
The best tip is: go get a computer science degree. The more
computer science you have, the better. You don't have to have a
CS degree, but it helps. It doesn't have to be an advanced
degree, but that helps too.
However, you're probably thinking of applying to Google a little
sooner than 2 to 8 years from now, so here are some shorter-term
tips for you.
Algorithm Complexity: you need to know Big-O. It's a must. If
you struggle with basic big-O complexity analysis, then you are
almost guaranteed not to get hired. It's, like, one chapter in
the beginning of one theory of computation book, so just go read
it. You can do it.
Sorting: know how to sort. Don't do bubble-sort. You should know
the details of at least one n*log(n) sorting algorithm,
preferably two (say, quicksort and merge sort). Merge sort can
be highly useful in situations where quicksort is impractical,
so take a look at it.
For God's sake, don't try sorting a linked list during the
interview.
Hashtables: hashtables are arguably the single most important
data structure known to mankind. You absolutely have to know how
they work. Again, it's like one chapter in one data structures
book, so just go read about them. You should be able to
implement one using only arrays in your favorite language, in
about the space of one interview.
Trees: you should know about trees. I'm tellin' ya: this is
basic stuff, and it's embarrassing to bring it up, but some of
you out there don't know basic tree construction, traversal and
manipulation algorithms. You should be familiar with binary
trees, n-ary trees, and trie-trees at the very very least. Trees
are probably the best source of practice problems for your
long-term warmup exercises.
You should be familiar with at least one flavor of balanced
binary tree, whether it's a red/black tree, a splay tree or an
AVL tree. You should actually know how it's implemented.
You should know about tree traversal algorithms: BFS and DFS,
and know the difference between inorder, postorder and preorder.
You might not use trees much day-to-day, but if so, it's because
you're avoiding tree problems. You won't need to do that anymore
once you know how they work. Study up!
Graphs
Graphs are, like, really really important. More than you think.
Even if you already think they're important, it's probably more
than you think.
There are three basic ways to represent a graph in memory
(objects and pointers, matrix, and adjacency list), and you
should familiarize yourself with each representation and its
pros and cons.
You should know the basic graph traversal algorithms:
breadth-first search and depth-first search. You should know
their computational complexity, their tradeoffs, and how to
implement them in real code.
You should try to study up on fancier algorithms, such as
Djikstra and A*, if you get a chance. They're really great for
just about anything, from game programming to distributed
computing to you name it. You should know them.
Whenever someone gives you a problem, think graphs. They are the
most fundamental and flexible way of representing any kind of a
relationship, so it's about a 50-50 shot that any interesting
design problem has a graph involved in it. Make absolutely sure
you can't think of a way to solve it using graphs before moving
on to other solution types. This tip is important!
Other data structures
You should study up on as many other data structures and
algorithms as you can fit in that big noggin of yours. You
should especially know about the most famous classes of
NP-complete problems, such as traveling salesman and the
knapsack problem, and be able to recognize them when an
interviewer asks you them in disguise.
You should find out what NP-complete means.
Basically, hit that data structures book hard, and try to retain
as much of it as you can, and you can't go wrong.
Math
Some interviewers ask basic discrete math questions. This is
more prevalent at Google than at other places I've been, and I
consider it a Good Thing, even though I'm not particularly good
at discrete math. We're surrounded by counting problems,
probability problems, and other Discrete Math 101 situations,
and those innumerate among us blithely hack around them without
knowing what we're doing.
Don't get mad if the interviewer asks math questions. Do your
best. Your best will be a heck of a lot better if you spend some
time before the interview refreshing your memory on (or teaching
yourself) the essentials of combinatorics and probability. You
should be familiar with n-choose-k problems and their ilk the
more the better.
I know, I know, you're short on time. But this tip can really
help make the difference between a "we're not sure" and a "let's
hire her". And it's actually not all that bad discrete math
doesn't use much of the high-school math you studied and forgot.
It starts back with elementary-school math and builds up from
there, so you can probably pick up what you need for interviews
in a couple of days of intense study.
Sadly, I don't have a good recommendation for a Discrete Math
book, so if you do, please mention it in the comments. Thanks.
Operating Systems
This is just a plug, from me, for you to know about processes,
threads and concurrency issues. A lot of interviewers ask about
that stuff, and it's pretty fundamental, so you should know it.
Know about locks and mutexes and semaphores and monitors and how
they work. Know about deadlock and livelock and how to avoid
them. Know what resources a processes needs, and a thread needs,
and how context switching works, and how it's initiated by the
operating system and underlying hardware. Know a little about
scheduling. The world is rapidly moving towards multi-core, and
you'll be a dinosaur in a real hurry if you don't understand the
fundamentals of "modern" (which is to say, "kinda broken")
concurrency constructs.
The best, most practical book I've ever personally read on the
subject is Doug Lea's Concurrent Programming in Java. It got me
the most bang per page. There are obviously lots of other books
on concurrency. I'd avoid the academic ones and focus on the
practical stuff, since it's most likely to get asked in
interviews.
Coding
You should know at least one programming language really well,
and it should preferably be C++ or Java. C# is OK too, since
it's pretty similar to Java. You will be expected to write some
code in at least some of your interviews. You will be expected
to know a fair amount of detail about your favorite programming
language.
Other Stuff
Because of the rules I outlined above, it's still possible that
you'll get Interviewer A, and none of the stuff you've studied
from these tips will be directly useful (except being warmed
up.) If so, just do your best. Worst case, you can always come
back in 6-12 months, right? Might seem like a long time, but I
assure you it will go by in a flash.
The stuff I've covered is actually mostly red-flags: stuff that
really worries people if you don't know it. The discrete math is
potentially optional, but somewhat risky if you don't know the
first thing about it. Everything else I've mentioned you should
know cold, and then you'll at least be prepped for the baseline
interview level. It could be a lot harder than that, depending
on the interviewer, or it could be easy.
It just depends on how lucky you are. Are you feeling lucky?
Then give it a try!
Send me your resume
I'll probably batch up any resume submissions people send me and
submit them weekly. In the meantime, study up! You have a lot of
warming up to do. Real-world work makes you rusty.
I hope this was helpful. Let the flames begin, etc. Yawn.
Love: The reality show
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