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Facebook Lost a Great Engineer

57 points by jorde 14y ago

codex 14y ago
Criticisms of the hiring process from those who didn't get hired are hard to take seriously--they may or may not be valid, but humans have a way of rationalizing defeat to protect their ego, and this cognitive dissonance tends to dent the defeated's perspective badly. You see this with any kind of objective test--IQ, SATs, etc. and, of course, subjective tests are subject to even more criticism. Unfortunately, those who passed their interviews have little reason to criticize the status quo. The best approach is a data-driven, experimental approach, of the kind likely to be taken by large companies. Small companies could do it too if they pooled their data.
Kiro 14y ago
"Solutions are in the sidenotes." Where are the sidenotes?
- tellarin 14y ago
  The sidenotes were too narrow? ;)
  - yen223 14y ago
    We'll just have to wait 400 years for the answer then
supercoder 14y ago
Yeah these sort of questions are pretty ridiculous. Though I wonder what the intent is here, say for the first question - "What is the pattern here ?" After looking up the solution on wikipedia - http://en.wikipedia.org/wiki/Look-and-say_sequence http://en.wikipedia.org/wiki/Look-and-say_sequence I would have to admit there is no way I'd figure that out without knowing the concept ahead of time. So are they looking for someone that knows the 'look and say sequence' explicitly ? Same way if you presented the meaning of numbers 80 or 443 to someone they'd either know or not, but not be able to guess. Or did they actually expect someone to work it out on the spot ?
- mattgreenrocks 14y ago
  > Or did they actually expect someone to work it out on the spot ? My hope is that they'd hope a candidate would be able to identify the connection to run length encoding within the pattern. Why do these puzzles emerge at big companies? It looks like a sort of institutional power trip emerges: "if you want to work with us, you need to be real good, and these are the sorts of problems we want you to think we deal with every day!" Except in most cases, they aren't, and there are plenty of mediocre folks already employed there. But the institution NEEDS to believe it only hires the best, and one way to perpetuate that belief is to haze new applicants more and more. All it really produces is candidates who are very lucky, or very compatible with the existing culture. Hiring is hard, and puzzles are a fail-fast mechanism that is terrible, but produces some sort of results, so it gets used.
  - johnmw 14y ago
    I think Cletus gave a good answer to why these questions are used in interviews in this post: http://news.ycombinator.com/item?id=5264510 http://news.ycombinator.com/item?id=5264510 In short, if you can't write a simple FizzBuzz program, then you are probably not a good developer. Questions like these are good for being a quick way to separate programmers from those who cannot program at all. But I agree - as someone who sucks at puzzles under pressure, questions like 'what's next after 111221?' seems like a totally retarded question to me.
    - mattgreenrocks 14y ago
      FizzBuzz is a legitimate litmus test for a candidate. It probably becomes a bit gauche once you get a bit of experience, however. In that case, I'd expect some sort of domain-specific technical question with some hand-holding to get the candidate talking. The idea is to coax the candidate into the problem.
- rbehrends 14y ago
  Yes, the problem with the look-and-say sequence is that it's not something that you can derive; it requires having the right insight. This makes it a bit different from other problems, where the interviewer is often not even so much interested in the solution, but in how you go about finding one. Many other sequence problems are amenable to a more systematic approach that at least tell them something about your problem-solving techniques. With the look-and-say sequence, you either see it or you don't. Regardless of whether you got it right or not, it doesn't tell an interviewer much about you, and is therefore not a good use of the limited time they have with you that could be used more productively.
brokentone 14y ago
Title made me think that one of their lead engineers died. Perhaps there would be a more accurate title option?
- BoyPopoy 14y ago
  damn right!
happywolf 14y ago
Writing an article to bash a company for not hiring him doesn't seem like what a great engineer would do.
- sergiosgc 14y ago
  Why not? I don't think it's healthful for a culture to impose a wide penalty on criticism. Criticism, if constructive, is not 100% negative. The post indeed criticizes Facebook, but also lays down an explanation of why Facebook's hiring practices are wrong. It contains useful information.
- przemoc 14y ago
  I'm not sure it's really a bashing. I read it as he's glad after all that facebook didn't hire him, so it's more like a message for those who already "lost" or will "lose" in puzzle-based hiring process. A message that states it's not necessarily their (i.e. prospective employees) loss in the end, and the more important part that it's not a reason they should feel bad about themselves after such "loss", because solving riddles is about solving riddles and not about finding good programmers (being one doesn't necessarily exclude having puzzle-solving ability, but it's not like a symmetric difference of these sets is empty, really, more like quite voluminous, I would say).
- BoyPopoy 14y ago
  That's what I'm about to say. He is a kid I had a developer just like him (I read his article this kid is not a team player at all I could tell). Anyway I fired my developer after 2 months because of his narcissistic programmer attitude.
- johnbellone 14y ago
  I agree completely. This could have been written in a way criticizing the hiring practices of companies where it didn't come off as a complete bashing. One thing you need to remember is that technical people that are performing phone screens are going to do a little research on you as a future candidate, and this isn't the first impression you want to make when vying for a job.
LookACamelToe 14y ago
Do you think they only failed you because you didn't know how to compute the square root? Did they tell you that you underperformed? There are tenths of reasons why a candidate might be rejected, outside of "did not perform well in tongue twisters". The fact that you got rejected does not mean that you suck. It means there is somebody who scored better feedback. He could have given the exact same answers like you, but better worded! Perhaps he would fit better with the FB culture! Maybe they failed you for your attitude? I mean, you made a post 2 years later saying "Ha! Look at me Mark!!! I am the king of the world!", good for you buddy. But I don't think anyone is going to weep for facebook's loss...
nbevans 14y ago
You'd have been just a cog in the machine at Facebook anyway. If you listen to some of their seasoned engineers speak they seem to take great satisfaction from delivering some inane and tiny little web app feature, seeing it through a year of testing, and seeing it in production. Whilst I'm sure that is satisfying if you've never known any different. It sure as hell isn't anywhere near as satisfying as building and scaling out a product or service of your own or one in which you are vested. The article is well written but you really shouldn't put Facebook on some sort of pedestal. Especially after two years, it seems like you still feel sore about it. It really isn't "all that" to work at Facebook. Do you really want to write PHP all day, for example? For an engineer it is more a bragging right and CV fodder than anything else.
dedsm 14y ago
"At my current company, we hire based on provable real-world experience." That is also a pretty bad hiring schema, you are leaving out a great deal of potential great programmers that are just starting, so, which strategy is better? I guess you always leave people behind, if it works for you, it's the right choice, and it has been working for facebook.
- johnbellone 14y ago
  Different hiring schemes work for different companies. Hell, even different teams within companies. If this works for FB there's a reason it is working. Job offers will come and go. Don't burn bridges that you may want to cross later in your career.
muratmutlu 14y ago
Good on you. This is a great way to look at it, nothing wrong with being confident of your value
Buzaga 14y ago
Arrows mapped to next/previous article ruined it for me...
mohoyt 14y ago
I understand that these questions can be ridiculous at times. But I think it is worth pointing out 2 things: 1) They may work well for a subset of applicants for a subset of companies. This, to some, is verification that these sorts of problems are a good way of narrowing down the applicant pool. Hence why they're used. 2) From Facebook (or any other employer)'s perspective, it's an incredibly hard job determining who will fit a given job specification. You may be great on paper, but be a total mismatch with regards to company ethos (I'm not saying you are, I'm just citing this as an example). The way (and that's assuming there is a particular way) of differentiating applicants and determining their suitability is not perfect. Different companies do it different ways, and all of this is constantly evolving. The fact that Facebook is using developers to conduct their interviews could be seen as progress to some compared to what there was x years ago in y company. It's never going to be perfect. The fact that you've moved on from this and done a bunch of great stuff is fantastic. It's Facebook's loss. But instead of just commenting on why their system sucks, and why it didn't work for you, why not make some constructive suggestions on how it might be improved.
- girvo 14y ago
  In my honest opinion, the way it can be improved is exactly the way my interview last Friday went: I walked in, and did the introductions. I had two programming problems to solve, but these weren't puzzles. The two questions were fairly simple, that used a lot of basic features of the language they use in this shop. The first question I couldn't remember the exact function names in the standard library (it's PHP, the stdlib is HUGE and stupid) but the interviewer helped me, and once I had the right functions in place, was easy. The second question tested OOP knowledge, and again was easy for any actual programmer. Then, once I'd passed that with flying colours, we moved on to the normal "interview". This week, I'm going in for a day (paid), to see if I'm a good culture fit, and look at the projects I'll be working on. I believe this is a brilliant way of interviewing and making sure you get the right candidate. Anyone who can't program will fail instantly (apparently thats a big problem here in Australia?), and then if the rest of the interview goes well, culture fit is actually TESTED (albeit as much as you can test in one day). I'm looking forward to this place actually :)
lucian1900 14y ago
I'm not sure you're right. I was rejected by Google after 2 phone interviews with somewhat similar questions and to this day I feel like it was a failure on my part. I really should have been able to do those puzzles better. I have a job I love now, but I don't feel like I deserve it. Overall, I suck. You probably do too.
tantaman 14y ago
Part of trying to get a job is learning about the interview practices of the company you are applying to. If they do puzzles then study some dumb puzzles. The puzzles usually aren't that hard and interviewers generally talk these types of problems over with you as you are solving them. If you really want to work at Facebook, and you are a conscientious developer, then you'll study and be prepared for their kind of interview.
PeterisP 14y ago
Well, the OP statement "write a function which merges two sorted arrays without allocating any additional memory. Aside from having no real-world value, it’s not actually possible" seems strange. Ok, any real-world usage might be applicable only in embedded systems which is a fairly narrow domain. Still, it is a small (easy to describe) problem that can be used to see how the applicant does problem solving for problems without a widely known best/proper solution - and that skill is probably 90% of any serious programming; the remainder is just typing while following an arbitrary syntax which a trained monkey can do. And the solution definitely exists - depending on how the interviewer wants output, you can either push the result out with a trivial iteration with a pointer on each array; or if the arrays aren't read only, you can sort them in-place with a slightly modified qsort or even bubblesort - both of these approaches don't need to allocate any memory on the heap, just 2 int counters in processor registers or stack.
- tantaman 14y ago
  The issue is merging the arrays, not sorting them. How do you MERGE two arrays without allocating a new one that is big enough to contain them both? If all you need to do is print what the result of the merge would be then sure, a solution does exist.
  - Inufu 14y ago
    Here's a solution that merges in place without any sorting: https://gist.github.com/Mononofu/5029975 https://gist.github.com/Mononofu/5029975 The basic idea is to use the (unused) beginning of array b as swap space for the beginning of array a. This swap space needs to be shifted around, so it's of course O(n^2). Still, it was fun to write. If you have termcolor installed ('sudo easy_install termcolor' on ubuntu), you'll see the arrays a and b as well as the swap space highlighted in color for each step. Example: http://dl.dropbox.com/u/2135523/2013022517.png http://dl.dropbox.com/u/2135523/2013022517.png
    - tantaman 14y ago
      Yep. I did say that that solution exists ^^. I just said that you couldn't do it without creating something to hold the merged result. Your solution does allocate a buffer to hold the merged result: `self.array = self.a + self.b` I wasn't saying you can't sort arrays in place (quicksort). I was saying you can't merge them in place. Somebody has to grow.
BoyPopoy 14y ago
Tyler they didn't hire you because you were not able to solve it. I'm a 100% sure it is because of your attitude the way you represented yourself to them on those interviews. Your article clearly tells me everything about you. I read your LinkedIN profile geeezzzz entrepreneur? you really? COME ON!!!!!!!!!
pramodliv1 14y ago
Yet another take on puzzles.. I reckon people are asked puzzles because if you can solve them, the probability of you solving real world problems is higher. Now that your raw intelligence/interest is proved, it's now a question of whether you have the tenacity to maintain huge codebases with your team
smoyer 14y ago
Is it possible that the look of distain on his face when the interviewer asked him to solve a puzzle indicated that he wasn't a good fit for their "puzzle culture"? I don't think it's fair to conclude he didn't get the FB job due to his failure to write a square root function. The funnier part is that this question isn't a puzzle (but does perhaps indicate how well the interviewee has internalized mathematics). I suspect I'd have failed him for ego ... "Today, after releasing 25 Github projects, creating several widely-used apps in less than a day each, and designing an entire architecture for a streaming platform, I realize I’m a pretty well-rounded and high-performing developer/engineer/architect. At the scale of Facebook, I’m exactly the sort of engineer I’d want many of." I've been in the industry for 30 years and realize I still have so much to learn.
- dguaraglia 14y ago
  Yeah, I think there's definitely an ego/butthurt attitude here I wouldn't put up with. Don't get me wrong, I think everyone needs to have a certain confidence on their abilities and expertise, but it works both ways: when hiring for our startup we'd look for honesty and humble acknowledgment of the candidate's shortcomings/lack of expertise. I wouldn't fail you for not knowing what the Newton's method for finding square roots is, but I will fail you for thinking it's irrelevant or not caring. If you don't care about my requirements in an interview, I don't think you'll do much better with actual work.
- tylermenezes 14y ago
  I actually did solve the square-root function problem, but I suspect too quickly because I did it from rote memory. I am fairly objectively the sort of programmer they would want in the sense they seemed to be selecting on. > This article is obviously somewhat over-stated. However, good programmers are aware of what they know and what they don't know, and maintaining a sense of imposter syndrome forever is somewhat counter-productive.
newobj 14y ago
I love the smell of hubris in the morning.
dlokshin 14y ago
A Finance sector perspective: In reading through the threads, there's a common underlying assumption that if you don't get the problem right, you won't get hired. That definitely is NOT the case in finance. We use the brain teasers and puzzles as a way to showcase how you think. For my interview, out of 5 brain teasers I nailed 2, was heavily helped through 2 more, and never got the last one, even with lots of help. But for each, the interviewer made it very clear that I was to think out loud. After getting the job, I later used the technique in interviews and gave positive reviews to those who had similarly struggled through puzzles but had used a similar thought process. In general we used this to weed out three different types of people: 1. Hard science majors who learned how to solve problems instead of think through problems. These people learned how to derive the heat diffusion equation, but would never put a story modeling a random walk in connection with that equation. 2. People who freeze when things get tough. Obviously a bad thing on the trade floor. While with coding you can often walk away from a hard problem, think about it, and come back, in finance, you can't walk away from losing lots of money over a short period of time ... you have to stop the bleeding. 3. People who learned how to think quickly and with rigorous process. The type of people you want.
raverbashing 14y ago
Sorry for the off topic but "How often do you expect candidates to write a function to calculate the square root of a number? I would fire any developer who chose to re-implement standard library functions." Not this crap again. Oh and he says he has an "interest in formal computer science" No, I don't expect you to reimplement square root. Or maybe I do, because that's what a lot of games do (or something similar) because you have to reach a balance between speed and accuracy. Or maybe because we need a bigger precision than a double, again there are libraries, but again we may need something else that's not in the library. So yes, absolutely, what I wouldn't hire is a "computer scientist" that can't work their way around a math problem. Edit: oh it gets worse, he gives the "never parse HTML without a proper HTML parser" talk Whine whine whine Step 1 - learn the rules. Step 2 - learn when to break them And it's only an example FB didn't lose a "great engineer", they were right on target.
miketwo 14y ago
Rephrase this as "Facebook Lost a Great Developer" and it begins to make sense, especially if Facebook was actually looking for a "Great Engineer". > I would fire any developer who chose to re-implement standard library functions. Who writes the standard library functions? > never parse HTML without a proper HTML parser Who writes the parsers? On merging arrays in-place: > Aside from having no real-world value, it’s not actually possible It is possible, and has value when dealing with large data sets, which I'm sure is a common issue at Facebook. Here's another way to look at it: "Given two sorted 0.5 terabyte arrays on a terabyte drive, and 1 gb of memory, merge the two arrays without an additional drive." There's no shame in not knowing or caring about things like this (it takes all kinds), but what the poster does (and seems to be good at) just may not be what Facebook was looking for. > At the scale of Facebook, I’m exactly the sort of engineer I’d want many of. Many possibly, but not only.
kirillzubovsky 14y ago
I hate puzzles too, but that's primarily because I never know the answers :) On a serious note though, it is quite possible that companies use puzzles as a screening technique because they are not looking for you. Specifically, they are looking for not you. Think about it, a big company needs an employee that would join them and work for at least 18 months in order to pay back the costs of hiring, but preferably stay for 3-4-5 years... as many as years as possible, if this is a good hacker we are talking about. Hiring someone who's likely to leave in 6 months is counter productive for a large company, and puzzles is one way to keep you away. You'd have to ask someone who was at Facebooks and Googles in their early days and see if the hiring was based on puzzles. I suspect in those times a lot of decisions were made in much similar ways to how you'd want to do it now. Puzzles are not the answer, and large companies would probably agree with you too, but it's a tool that seems to work best for them and it's scalable to achieve a consisten outcome over a long term horizon. Precisely what large companies need.
lynchdt 14y ago
You did not get the job because of your attitude. "...I realize I’m a pretty well-rounded and high-performing developer/engineer/architect. At the scale of Facebook, I’m exactly the sort of engineer I’d want many of...." In my opinion there are at least three no-hire red flags attached to this statement.
Ashoat 14y ago
"which merges two sorted arrays without allocating any additional memory. Aside from having no real-world value, it's not actually possible, and his solution code clobbered most of the data in the first array." This is referring to me. The author has misrepresented the truth. (1) The problem does not state that you may not allocate additional memory; only that the memory allocated must be constant relative to the size of your input. (2) Given #1, this problem is absolutely possible. (3) The problem explicitly asks you to merge the two arrays "in place". If by "clobbered" you mean changed, then that means that by definition one of the arrays will be "clobbered". We can certainly have a separate conversation about whether modifying structures in place is a good coding practice, but it is generally more efficient and highly widespread in non-functional languages. I'm sure it wasn't purposeful, but I'm disappointed that the author misrepresented our conversation to make a point. Separately: (4) This problem is extremely applicable to real-life programming IMHO. It does not use any esoteric data structures. It does not use any complicated algorithms. All you need to do is iterate through two arrays at the same time. A great majority of candidates have solved this problem. In general I agree with this post's thesis. Facebook's general philosophy with interviews is to allow each interviewer to ask whatever questions they want, and the consequence is a variance in the type of questions getting asked. However, based on internal conversations I know that Facebook is trying to move away from "puzzle" questions by explicitly "retiring" a number of questions that we consider to be unproductive.
- nilkn 14y ago
  This is a slightly awkward friendship you have with the author of the post.
  - Ashoat 14y ago
    Don't worry, I promise we're actually homies ;) We talked it through and he removed the part that bothered me. I'm actually gonna hang out with him tonight...
BenjaminN 14y ago
Tyler, I have two things to say about this. 1°) I think you don't get it: when you're Facebook, Google or any other company receiving and interviewing thousands of candidates for a job, you're having a different hiring strategy than a small startup. Their strategy is "hiring a bad programmer costs us more than rejecting a good one". So they tend to reject good programmers, but they mostly reject bad programmers. In the end: they only hire good programmers, and that's what matters. In contrast, startups are having the "it costs us more to reject a good programmer than to hire a bad one" strategy. So they hire more easily, most of the time, even if in the end they hire average/bad programmers, they don't care. 2°) I was interviewed for a front-end job at facebook, and I didn't get in. I think I'm not the best programmer around, but I'm okay, and I would do a great job at facebook. And just so you know : my first interview question was way way way harder than any of your questions. I think those puzzles are a good way to spot good programmers amongst thousands of good/average/bad programmers. I'll give you a really simple example: find the highest number in an array. You can find it using several different ways, but if you just go through the whole array, you might be a good programmer, but the next person I'd interview might be one too, and he will find it with a much lower complexity. I'd hire him. Simple as that. Bottom line — here's the question I was asked at facebook : you have a matrix of letters, and you have to find all the words you can do with it. For a front-end/product design job. And I'm not posting an article saying they suck at hiring.
- Schwolop 14y ago
  Without any other information, how can you possibly implement max() without going through the whole array?

57 points by jorde 14y ago

codex 14y ago

Criticisms of the hiring process from those who didn't get hired are hard to take seriously--they may or may not be valid, but humans have a way of rationalizing defeat to protect their ego, and this cognitive dissonance tends to dent the defeated's perspective badly. You see this with any kind of objective test--IQ, SATs, etc. and, of course, subjective tests are subject to even more criticism. Unfortunately, those who passed their interviews have little reason to criticize the status quo. The best approach is a data-driven, experimental approach, of the kind likely to be taken by large companies. Small companies could do it too if they pooled their data.

Kiro 14y ago

"Solutions are in the sidenotes." Where are the sidenotes?

tellarin 14y ago
The sidenotes were too narrow? ;)
- yen223 14y ago
  We'll just have to wait 400 years for the answer then

supercoder 14y ago

Yeah these sort of questions are pretty ridiculous. Though I wonder what the intent is here, say for the first question - "What is the pattern here ?" After looking up the solution on wikipedia - http://en.wikipedia.org/wiki/Look-and-say_sequence http://en.wikipedia.org/wiki/Look-and-say_sequence I would have to admit there is no way I'd figure that out without knowing the concept ahead of time. So are they looking for someone that knows the 'look and say sequence' explicitly ? Same way if you presented the meaning of numbers 80 or 443 to someone they'd either know or not, but not be able to guess. Or did they actually expect someone to work it out on the spot ?

mattgreenrocks 14y ago
> Or did they actually expect someone to work it out on the spot ? My hope is that they'd hope a candidate would be able to identify the connection to run length encoding within the pattern. Why do these puzzles emerge at big companies? It looks like a sort of institutional power trip emerges: "if you want to work with us, you need to be real good, and these are the sorts of problems we want you to think we deal with every day!" Except in most cases, they aren't, and there are plenty of mediocre folks already employed there. But the institution NEEDS to believe it only hires the best, and one way to perpetuate that belief is to haze new applicants more and more. All it really produces is candidates who are very lucky, or very compatible with the existing culture. Hiring is hard, and puzzles are a fail-fast mechanism that is terrible, but produces some sort of results, so it gets used.
- johnmw 14y ago
  I think Cletus gave a good answer to why these questions are used in interviews in this post: http://news.ycombinator.com/item?id=5264510 http://news.ycombinator.com/item?id=5264510 In short, if you can't write a simple FizzBuzz program, then you are probably not a good developer. Questions like these are good for being a quick way to separate programmers from those who cannot program at all. But I agree - as someone who sucks at puzzles under pressure, questions like 'what's next after 111221?' seems like a totally retarded question to me.
  - mattgreenrocks 14y ago
    FizzBuzz is a legitimate litmus test for a candidate. It probably becomes a bit gauche once you get a bit of experience, however. In that case, I'd expect some sort of domain-specific technical question with some hand-holding to get the candidate talking. The idea is to coax the candidate into the problem.
rbehrends 14y ago
Yes, the problem with the look-and-say sequence is that it's not something that you can derive; it requires having the right insight. This makes it a bit different from other problems, where the interviewer is often not even so much interested in the solution, but in how you go about finding one. Many other sequence problems are amenable to a more systematic approach that at least tell them something about your problem-solving techniques. With the look-and-say sequence, you either see it or you don't. Regardless of whether you got it right or not, it doesn't tell an interviewer much about you, and is therefore not a good use of the limited time they have with you that could be used more productively.

brokentone 14y ago

Title made me think that one of their lead engineers died. Perhaps there would be a more accurate title option?

BoyPopoy 14y ago
damn right!

happywolf 14y ago

Writing an article to bash a company for not hiring him doesn't seem like what a great engineer would do.

sergiosgc 14y ago
Why not? I don't think it's healthful for a culture to impose a wide penalty on criticism. Criticism, if constructive, is not 100% negative. The post indeed criticizes Facebook, but also lays down an explanation of why Facebook's hiring practices are wrong. It contains useful information.
przemoc 14y ago
I'm not sure it's really a bashing. I read it as he's glad after all that facebook didn't hire him, so it's more like a message for those who already "lost" or will "lose" in puzzle-based hiring process. A message that states it's not necessarily their (i.e. prospective employees) loss in the end, and the more important part that it's not a reason they should feel bad about themselves after such "loss", because solving riddles is about solving riddles and not about finding good programmers (being one doesn't necessarily exclude having puzzle-solving ability, but it's not like a symmetric difference of these sets is empty, really, more like quite voluminous, I would say).
BoyPopoy 14y ago
That's what I'm about to say. He is a kid I had a developer just like him (I read his article this kid is not a team player at all I could tell). Anyway I fired my developer after 2 months because of his narcissistic programmer attitude.
johnbellone 14y ago
I agree completely. This could have been written in a way criticizing the hiring practices of companies where it didn't come off as a complete bashing. One thing you need to remember is that technical people that are performing phone screens are going to do a little research on you as a future candidate, and this isn't the first impression you want to make when vying for a job.

LookACamelToe 14y ago

Do you think they only failed you because you didn't know how to compute the square root? Did they tell you that you underperformed? There are tenths of reasons why a candidate might be rejected, outside of "did not perform well in tongue twisters". The fact that you got rejected does not mean that you suck. It means there is somebody who scored better feedback. He could have given the exact same answers like you, but better worded! Perhaps he would fit better with the FB culture! Maybe they failed you for your attitude? I mean, you made a post 2 years later saying "Ha! Look at me Mark!!! I am the king of the world!", good for you buddy. But I don't think anyone is going to weep for facebook's loss...

nbevans 14y ago

You'd have been just a cog in the machine at Facebook anyway. If you listen to some of their seasoned engineers speak they seem to take great satisfaction from delivering some inane and tiny little web app feature, seeing it through a year of testing, and seeing it in production. Whilst I'm sure that is satisfying if you've never known any different. It sure as hell isn't anywhere near as satisfying as building and scaling out a product or service of your own or one in which you are vested. The article is well written but you really shouldn't put Facebook on some sort of pedestal. Especially after two years, it seems like you still feel sore about it. It really isn't "all that" to work at Facebook. Do you really want to write PHP all day, for example? For an engineer it is more a bragging right and CV fodder than anything else.

dedsm 14y ago

"At my current company, we hire based on provable real-world experience." That is also a pretty bad hiring schema, you are leaving out a great deal of potential great programmers that are just starting, so, which strategy is better? I guess you always leave people behind, if it works for you, it's the right choice, and it has been working for facebook.

johnbellone 14y ago
Different hiring schemes work for different companies. Hell, even different teams within companies. If this works for FB there's a reason it is working. Job offers will come and go. Don't burn bridges that you may want to cross later in your career.

muratmutlu 14y ago

Good on you. This is a great way to look at it, nothing wrong with being confident of your value

Buzaga 14y ago

Arrows mapped to next/previous article ruined it for me...

mohoyt 14y ago

I understand that these questions can be ridiculous at times. But I think it is worth pointing out 2 things: 1) They may work well for a subset of applicants for a subset of companies. This, to some, is verification that these sorts of problems are a good way of narrowing down the applicant pool. Hence why they're used. 2) From Facebook (or any other employer)'s perspective, it's an incredibly hard job determining who will fit a given job specification. You may be great on paper, but be a total mismatch with regards to company ethos (I'm not saying you are, I'm just citing this as an example). The way (and that's assuming there is a particular way) of differentiating applicants and determining their suitability is not perfect. Different companies do it different ways, and all of this is constantly evolving. The fact that Facebook is using developers to conduct their interviews could be seen as progress to some compared to what there was x years ago in y company. It's never going to be perfect. The fact that you've moved on from this and done a bunch of great stuff is fantastic. It's Facebook's loss. But instead of just commenting on why their system sucks, and why it didn't work for you, why not make some constructive suggestions on how it might be improved.

girvo 14y ago
In my honest opinion, the way it can be improved is exactly the way my interview last Friday went: I walked in, and did the introductions. I had two programming problems to solve, but these weren't puzzles. The two questions were fairly simple, that used a lot of basic features of the language they use in this shop. The first question I couldn't remember the exact function names in the standard library (it's PHP, the stdlib is HUGE and stupid) but the interviewer helped me, and once I had the right functions in place, was easy. The second question tested OOP knowledge, and again was easy for any actual programmer. Then, once I'd passed that with flying colours, we moved on to the normal "interview". This week, I'm going in for a day (paid), to see if I'm a good culture fit, and look at the projects I'll be working on. I believe this is a brilliant way of interviewing and making sure you get the right candidate. Anyone who can't program will fail instantly (apparently thats a big problem here in Australia?), and then if the rest of the interview goes well, culture fit is actually TESTED (albeit as much as you can test in one day). I'm looking forward to this place actually :)

lucian1900 14y ago

I'm not sure you're right. I was rejected by Google after 2 phone interviews with somewhat similar questions and to this day I feel like it was a failure on my part. I really should have been able to do those puzzles better. I have a job I love now, but I don't feel like I deserve it. Overall, I suck. You probably do too.

tantaman 14y ago

Part of trying to get a job is learning about the interview practices of the company you are applying to. If they do puzzles then study some dumb puzzles. The puzzles usually aren't that hard and interviewers generally talk these types of problems over with you as you are solving them. If you really want to work at Facebook, and you are a conscientious developer, then you'll study and be prepared for their kind of interview.

PeterisP 14y ago

Well, the OP statement "write a function which merges two sorted arrays without allocating any additional memory. Aside from having no real-world value, it’s not actually possible" seems strange. Ok, any real-world usage might be applicable only in embedded systems which is a fairly narrow domain. Still, it is a small (easy to describe) problem that can be used to see how the applicant does problem solving for problems without a widely known best/proper solution - and that skill is probably 90% of any serious programming; the remainder is just typing while following an arbitrary syntax which a trained monkey can do. And the solution definitely exists - depending on how the interviewer wants output, you can either push the result out with a trivial iteration with a pointer on each array; or if the arrays aren't read only, you can sort them in-place with a slightly modified qsort or even bubblesort - both of these approaches don't need to allocate any memory on the heap, just 2 int counters in processor registers or stack.

tantaman 14y ago
The issue is merging the arrays, not sorting them. How do you MERGE two arrays without allocating a new one that is big enough to contain them both? If all you need to do is print what the result of the merge would be then sure, a solution does exist.
- Inufu 14y ago
  Here's a solution that merges in place without any sorting: https://gist.github.com/Mononofu/5029975 https://gist.github.com/Mononofu/5029975 The basic idea is to use the (unused) beginning of array b as swap space for the beginning of array a. This swap space needs to be shifted around, so it's of course O(n^2). Still, it was fun to write. If you have termcolor installed ('sudo easy_install termcolor' on ubuntu), you'll see the arrays a and b as well as the swap space highlighted in color for each step. Example: http://dl.dropbox.com/u/2135523/2013022517.png http://dl.dropbox.com/u/2135523/2013022517.png
  - tantaman 14y ago
    Yep. I did say that that solution exists ^^. I just said that you couldn't do it without creating something to hold the merged result. Your solution does allocate a buffer to hold the merged result: `self.array = self.a + self.b` I wasn't saying you can't sort arrays in place (quicksort). I was saying you can't merge them in place. Somebody has to grow.

BoyPopoy 14y ago

Tyler they didn't hire you because you were not able to solve it. I'm a 100% sure it is because of your attitude the way you represented yourself to them on those interviews. Your article clearly tells me everything about you. I read your LinkedIN profile geeezzzz entrepreneur? you really? COME ON!!!!!!!!!

pramodliv1 14y ago

Yet another take on puzzles.. I reckon people are asked puzzles because if you can solve them, the probability of you solving real world problems is higher. Now that your raw intelligence/interest is proved, it's now a question of whether you have the tenacity to maintain huge codebases with your team

smoyer 14y ago

Is it possible that the look of distain on his face when the interviewer asked him to solve a puzzle indicated that he wasn't a good fit for their "puzzle culture"? I don't think it's fair to conclude he didn't get the FB job due to his failure to write a square root function. The funnier part is that this question isn't a puzzle (but does perhaps indicate how well the interviewee has internalized mathematics). I suspect I'd have failed him for ego ... "Today, after releasing 25 Github projects, creating several widely-used apps in less than a day each, and designing an entire architecture for a streaming platform, I realize I’m a pretty well-rounded and high-performing developer/engineer/architect. At the scale of Facebook, I’m exactly the sort of engineer I’d want many of." I've been in the industry for 30 years and realize I still have so much to learn.

dguaraglia 14y ago
Yeah, I think there's definitely an ego/butthurt attitude here I wouldn't put up with. Don't get me wrong, I think everyone needs to have a certain confidence on their abilities and expertise, but it works both ways: when hiring for our startup we'd look for honesty and humble acknowledgment of the candidate's shortcomings/lack of expertise. I wouldn't fail you for not knowing what the Newton's method for finding square roots is, but I will fail you for thinking it's irrelevant or not caring. If you don't care about my requirements in an interview, I don't think you'll do much better with actual work.
tylermenezes 14y ago
I actually did solve the square-root function problem, but I suspect too quickly because I did it from rote memory. I am fairly objectively the sort of programmer they would want in the sense they seemed to be selecting on. > This article is obviously somewhat over-stated. However, good programmers are aware of what they know and what they don't know, and maintaining a sense of imposter syndrome forever is somewhat counter-productive.

newobj 14y ago

I love the smell of hubris in the morning.

dlokshin 14y ago

A Finance sector perspective: In reading through the threads, there's a common underlying assumption that if you don't get the problem right, you won't get hired. That definitely is NOT the case in finance. We use the brain teasers and puzzles as a way to showcase how you think. For my interview, out of 5 brain teasers I nailed 2, was heavily helped through 2 more, and never got the last one, even with lots of help. But for each, the interviewer made it very clear that I was to think out loud. After getting the job, I later used the technique in interviews and gave positive reviews to those who had similarly struggled through puzzles but had used a similar thought process. In general we used this to weed out three different types of people: 1. Hard science majors who learned how to solve problems instead of think through problems. These people learned how to derive the heat diffusion equation, but would never put a story modeling a random walk in connection with that equation. 2. People who freeze when things get tough. Obviously a bad thing on the trade floor. While with coding you can often walk away from a hard problem, think about it, and come back, in finance, you can't walk away from losing lots of money over a short period of time ... you have to stop the bleeding. 3. People who learned how to think quickly and with rigorous process. The type of people you want.

raverbashing 14y ago

Sorry for the off topic but "How often do you expect candidates to write a function to calculate the square root of a number? I would fire any developer who chose to re-implement standard library functions." Not this crap again. Oh and he says he has an "interest in formal computer science" No, I don't expect you to reimplement square root. Or maybe I do, because that's what a lot of games do (or something similar) because you have to reach a balance between speed and accuracy. Or maybe because we need a bigger precision than a double, again there are libraries, but again we may need something else that's not in the library. So yes, absolutely, what I wouldn't hire is a "computer scientist" that can't work their way around a math problem. Edit: oh it gets worse, he gives the "never parse HTML without a proper HTML parser" talk Whine whine whine Step 1 - learn the rules. Step 2 - learn when to break them And it's only an example FB didn't lose a "great engineer", they were right on target.

miketwo 14y ago

Rephrase this as "Facebook Lost a Great Developer" and it begins to make sense, especially if Facebook was actually looking for a "Great Engineer". > I would fire any developer who chose to re-implement standard library functions. Who writes the standard library functions? > never parse HTML without a proper HTML parser Who writes the parsers? On merging arrays in-place: > Aside from having no real-world value, it’s not actually possible It is possible, and has value when dealing with large data sets, which I'm sure is a common issue at Facebook. Here's another way to look at it: "Given two sorted 0.5 terabyte arrays on a terabyte drive, and 1 gb of memory, merge the two arrays without an additional drive." There's no shame in not knowing or caring about things like this (it takes all kinds), but what the poster does (and seems to be good at) just may not be what Facebook was looking for. > At the scale of Facebook, I’m exactly the sort of engineer I’d want many of. Many possibly, but not only.

kirillzubovsky 14y ago

I hate puzzles too, but that's primarily because I never know the answers :) On a serious note though, it is quite possible that companies use puzzles as a screening technique because they are not looking for you. Specifically, they are looking for not you. Think about it, a big company needs an employee that would join them and work for at least 18 months in order to pay back the costs of hiring, but preferably stay for 3-4-5 years... as many as years as possible, if this is a good hacker we are talking about. Hiring someone who's likely to leave in 6 months is counter productive for a large company, and puzzles is one way to keep you away. You'd have to ask someone who was at Facebooks and Googles in their early days and see if the hiring was based on puzzles. I suspect in those times a lot of decisions were made in much similar ways to how you'd want to do it now. Puzzles are not the answer, and large companies would probably agree with you too, but it's a tool that seems to work best for them and it's scalable to achieve a consisten outcome over a long term horizon. Precisely what large companies need.

lynchdt 14y ago

You did not get the job because of your attitude. "...I realize I’m a pretty well-rounded and high-performing developer/engineer/architect. At the scale of Facebook, I’m exactly the sort of engineer I’d want many of...." In my opinion there are at least three no-hire red flags attached to this statement.

Ashoat 14y ago

"which merges two sorted arrays without allocating any additional memory. Aside from having no real-world value, it's not actually possible, and his solution code clobbered most of the data in the first array." This is referring to me. The author has misrepresented the truth. (1) The problem does not state that you may not allocate additional memory; only that the memory allocated must be constant relative to the size of your input. (2) Given #1, this problem is absolutely possible. (3) The problem explicitly asks you to merge the two arrays "in place". If by "clobbered" you mean changed, then that means that by definition one of the arrays will be "clobbered". We can certainly have a separate conversation about whether modifying structures in place is a good coding practice, but it is generally more efficient and highly widespread in non-functional languages. I'm sure it wasn't purposeful, but I'm disappointed that the author misrepresented our conversation to make a point. Separately: (4) This problem is extremely applicable to real-life programming IMHO. It does not use any esoteric data structures. It does not use any complicated algorithms. All you need to do is iterate through two arrays at the same time. A great majority of candidates have solved this problem. In general I agree with this post's thesis. Facebook's general philosophy with interviews is to allow each interviewer to ask whatever questions they want, and the consequence is a variance in the type of questions getting asked. However, based on internal conversations I know that Facebook is trying to move away from "puzzle" questions by explicitly "retiring" a number of questions that we consider to be unproductive.

nilkn 14y ago
This is a slightly awkward friendship you have with the author of the post.
- Ashoat 14y ago
  Don't worry, I promise we're actually homies ;) We talked it through and he removed the part that bothered me. I'm actually gonna hang out with him tonight...

BenjaminN 14y ago

Tyler, I have two things to say about this. 1°) I think you don't get it: when you're Facebook, Google or any other company receiving and interviewing thousands of candidates for a job, you're having a different hiring strategy than a small startup. Their strategy is "hiring a bad programmer costs us more than rejecting a good one". So they tend to reject good programmers, but they mostly reject bad programmers. In the end: they only hire good programmers, and that's what matters. In contrast, startups are having the "it costs us more to reject a good programmer than to hire a bad one" strategy. So they hire more easily, most of the time, even if in the end they hire average/bad programmers, they don't care. 2°) I was interviewed for a front-end job at facebook, and I didn't get in. I think I'm not the best programmer around, but I'm okay, and I would do a great job at facebook. And just so you know : my first interview question was way way way harder than any of your questions. I think those puzzles are a good way to spot good programmers amongst thousands of good/average/bad programmers. I'll give you a really simple example: find the highest number in an array. You can find it using several different ways, but if you just go through the whole array, you might be a good programmer, but the next person I'd interview might be one too, and he will find it with a much lower complexity. I'd hire him. Simple as that. Bottom line — here's the question I was asked at facebook : you have a matrix of letters, and you have to find all the words you can do with it. For a front-end/product design job. And I'm not posting an article saying they suck at hiring.

Schwolop 14y ago
Without any other information, how can you possibly implement max() without going through the whole array?