8 ms·

> I think this is a good question, because it is an abstract version of the kind of problems that any non trivial code has to address. It is easy to describe, a

> I think this is a good question, because it is an abstract version of the kind of problems that any non trivial code has to address. It is easy to describe, and easy to solve if you know what you are doing. I don't use it anymore because it's too common to be useful. This is precisely the problem the OP is talking about. When's the last time you ever did anything as low level as reversing a linked list? It's a solved problem, and something an employee would NEVER do in your company, let alone search for the optimal solution in 10 stressful minutes while you breathe down his neck. > And yet, through the years I've gotten the feedback[0] that it is "far detached from real work", "tests how good I did in school rather than how good I am" and various other comments -- and almost always from candidates who did poorly; I've never gotten this feedback from anyone I would consider competent. Major red flag. I don't mean to be rude, but this sentence comes off as very arrogant. > I don't, in general, trust direct feedback from someone I turned down (or hired, for that matter). Why? Because they're in a lower caste? If you can't handle direct feedback, you're a terrible manager.

theprotocol 9y ago
>This is precisely the problem the OP is talking about. When's the last time you ever did anything as low level as reversing a linked list? It's a solved problem, and something an employee would NEVER do in your company, let alone search for the optimal solution in 10 stressful minutes while you breathe down his neck. The thing about such things is I know I can do it. But maybe it'll take 5 minutes, or maybe an hour. Maybe I'd attempt to do it differently given an unfamiliar scenario for which to be doing this in the first place; maybe I've never done this specific task in this specific language, and I'll take some extra minutes figuring out how pointers or references work in the language I'm using in the test. Maybe I've recently enjoyed some momentum on high level concepts (i.e. I produced software that fulfills a business need) and it'll take me a while to refocus my attention on low level implementations. Engaging one's brain carries some very variable overheads. If you just give me 5 minutes and watch me write every single line of code and comment about it while I'm doing it, then it's just not going to happen.
- burgerdev 9y ago
  You guys do realize that reversing a linked list is not 'solving a difficult programming puzzle'? Seeing the number of applicants that can't read lines from a file (in any given language), I'd say this question is adequate if you want to employ someone with programming experience.
  - theprotocol 9y ago
    You're right about that particular exercise. I kind of used it to make a more general point.
- beagle3 9y ago
  Indeed. For the record, I let people take however much time they need, if they get stuck I ask them to discuss their approach, etc. I'm not looking for the solution (as parent said, it is a solved problem), I'm looking for evidence of problem solving skills. And you can demonstrate them, even for this question, without actually being able to write down a working solution. (I don't want to go into everything here, but one of the things I look for is people who consider the case of an empty list - critically thinking about special cases is an important trait) That said, work environment often has some kind of time constraint. If one can't solve any of the (simple, abstract, representative) problems that I pose within a 2hour time frame, it is possible that they are not a good match. And unfortunately, I rarely have the leisure to hire someone for a month to prove otherwise. [from a comment of yours below] > You're right about that particular exercise. I kind of used it to make a more general point. That may be true for others, but my interview questions are all of this mold: abstract, with a short and simple (but not trick-required-here) solution, close to (an abstract version of) a real world "business problem". I agree that technical interview questions (much like many aspects of life) put the wrong kind of stress on some and puts them at a disadvantage. But, and I always ask this[0], what alternative do you suggest? [0] The answers so far have been essentially either "no idea", "let me prove to you on my terms" (which, when broken down, is rarely economical for either side or at all possible), or "just trust me on this"; I find none of them satisfying.
  - 9y ago
ThrowawayR2 9y ago
> When's the last time you ever did anything as low level as reversing a linked list? It's a topic covered in a sophomore-level data structures course over just a few days. If a college sophomore can pick it up that quickly (and "sophomoric" is a word for a reason), it should be no problem for a seasoned programmer to (re-)learn it in a couple of hours.
- kstenerud 9y ago
  How about in 10 minutes at a whiteboard while the interviewer waits patiently to judge you?
- deleted 9y ago
  [deleted]
sago 9y ago
> When's the last time you ever did anything as low level as reversing a linked list? It's a solved problem, and something an employee would NEVER do in your company I think that misses the point. A linked list is a simple data structure that needs little explanation, and yet uses indirection in a way that can get you into trouble. As such, it is a great toy problem to asses a person's ability to work with linked data. Reversing a list, is similarly, very simple to explain, and a quite rudimentary operation. So if I'm trying to asses basic ability to manipulate data in code, it seems much simpler than trying to give them a real-world linked data structure and have them do a real-world manipulation on it. The real problem is the assumption that this is a 'solved problem', i.e. that a) there is an one-true-way algorithm out there, and b) that is what the interviewer wants you to know (i.e. know in the sense of knowing a fact). That is true of too many interviewers, and that is the problem. I can imagine setting that as a question in an interview. And I wouldn't be interested in 'the algorithm', I'd want to see that someone could figure it out easily. If someone came in and clearly had just learnt it, it would tell me nothing. I would immediately ask them something else to take them out of their rote prep. But if someone came in and couldn't figure it out, why would I think they'd be any better on 'unsolved problems'? In terms of being able to manipulate data, it isn't much beyond Fizzbuzz. The 'it's a solved problem' attitude smacks of leftpad thinking to me.
- kevan 9y ago
  Exactly. As an interviewer I don't get any data if you have an algorithm memorized and throw it on the board. I'm trying to assess critical thinking and problem-solving skills, I've voted to hire many people who clearly had never seen the problem before, didn't get a working solution in the time we had, but demonstrated great problem-solving approach.
- crdoconnor 9y ago
  I almost exclusively give candidates realistic tasks (slightly modified real world tasks) and give them under realistic conditions (free access to google, candidate's own laptop preferably). It perplexes me. What do you gain by not doing that?
  - 9y ago
temac 9y ago
Yep, you have the "far detached from real work" reaction. Plus, if you consider "you" (or an imaginary candidate you project yourself upon) risk not being able to answer it in 10 minutes because of such the high pressure it would put on you, then it basically means that you did not even try to answer it in your head, or that you were not able to. But this is the moral equivalent of asking a person who pretends to be a mathematician to do a 3 by 3 figures multiplication. It won't show much if they answer correctly (at least demonstrate a correct method to do it, never mind potential mistakes), but you can easily dismiss them if they fail. Now programming is a little bit different, because I admit there can be some positions where people can somehow contribute despite being incapable of lots of basic things. It depends on several factors, though, and even then I'm not sure the end result would ever be very solid. But I understand that in some contexts, such people would not be hired...
beagle3 9y ago
Wow, it appears my point was completely missed (and I was otherwise painted as a bigot), so let me try to explain better. > It's a solved problem, and something an employee would NEVER do in your company, let alone search for the optimal solution in 10 stressful minutes while you breathe down his neck. Actually, just a couple of weeks ago we had something almost equivalent, that involved chasing "pointers" through databases and files. It was for less than 1M cases, but still - any O(n^2) solution would have been infeasible (and an nlogn solution about 20 times slower than an O(n) solution; in this case, it was a one-off, and the difference would have been between 1hr of runtime and 1day of runtime). > When's the last time you ever did anything as low level as reversing a linked list? Please re-read what I wrote. I wrote, in fact, "you (almost) never need to reverse linked lists in practice". I also explained that it is an abstract version of a kind of thing that DOES happen often. > Major red flag. I don't mean to be rude, but this sentence comes off as very arrogant. Perhaps. For all you know, I'm a dog, but I'll say that I'm soon entering my 4th decade in the industry, I'm well respected, I've hired (and fired) tens of people through the years (and interviewed hundreds if not thousands); and I'm well respected among my peers for having very accurate evaluations of people's abilities. I do not aim to be politically correct. > Why? Because they're in a lower caste? If you can't handle direct feedback, you're a terrible manager. No, because I've just hired them, or just didn't hire them; either way, I think it is irresponsible to trust the statement of a person I don't actually know and who may either hold a grudge or want to please me right now. I meant to say "direct immediate feedback", which is perhaps better wording. After I know a person, I ask them (and usually get) the most direct and raw feedback I can get.
- kstenerud 9y ago
  > it was a one-off, and the difference would have been between 1hr of runtime and 1day of runtime). What's wrong with 1h vs 1d for a one-off thing? Your effective delivery time would be close enough to equivalent after all the administrative BS and customer expectations, and a naive approach piss simple to verify. If it was going to mean the difference between 1h and multiple days, here's what I'd do: - Fire up my trusty browser. - Navigate to google.com - Type in "reverse a linked list" - Evaluate all of the solutions I find and pick the best efficiency / verifiability match to solve the problem in a reasonable amount of time. Are you going to test that in an interview question? No, you're going to effectively "whiteboard" me, asking me to reinvent the wheel on the spot. And I'm going to resent you for it. > but I'll say that I'm soon entering my 4th decade in the industry, I'm well respected, I've hired (and fired) tens of people through the years (and interviewed hundreds if not thousands); and I'm well respected among my peers for having very accurate evaluations of people's abilities. I do not aim to be politically correct. And I'm in my third decade in the industry, all the respect, blah, blah, half a million lines of open source in the wild. So what? You can make the same mistakes over and over in any industry and never think to question if you're doing it wrong. This is ESPECIALLY problematic when it comes to people skills. > No, because I've just hired them, or just didn't hire them; either way, I think it is irresponsible to trust the statement of a person I don't actually know and who may either hold a grudge or want to please me right now. It's the PERFECT time to ask them, because it's fresh in their mind. A skilled interrogator can get information despite the subject's frame of mind. I'm actually surprised that you assume everyone you accept or reject is either going to be a sycophant or hold a grudge. You WANT them to talk while the frustrations they encountered are still fresh in their minds. That's the most raw feedback you'll ever get. You really do need to start treating them like human beings. Wanna know how I evaluated potential game devs in person? I asked them what dev environment they were most comfortable in, gave them a computer hooked up to the internet and a picture of a tweetie bird, and said "Make the bird jump. Use google to look shit up." Worked amazingly well.
joshjje 9y ago
Im not sure I agree with the premise that interview questions like that that may never come up in the job are useless. To me it doesnt matter. They are easily solvable and any competent programmer should be able to solve them. Of course I think more relevant questions are obviously better.
watwut 9y ago
> When's the last time you ever did anything as low level as reversing a linked list? It's a solved problem, and something an employee would NEVER do in your company, let alone search for the optimal solution in 10 stressful minutes while you breathe down his neck. I need occasional semi ad-hoc datastructures and manipulations like that. The requirement is never "reverse the list", but it is often something like "this api here needs input in opposite order and data happen to be in list". I would not see reverse the list as something specially unusual.

theprotocol 9y ago

>This is precisely the problem the OP is talking about. When's the last time you ever did anything as low level as reversing a linked list? It's a solved problem, and something an employee would NEVER do in your company, let alone search for the optimal solution in 10 stressful minutes while you breathe down his neck. The thing about such things is I know I can do it. But maybe it'll take 5 minutes, or maybe an hour. Maybe I'd attempt to do it differently given an unfamiliar scenario for which to be doing this in the first place; maybe I've never done this specific task in this specific language, and I'll take some extra minutes figuring out how pointers or references work in the language I'm using in the test. Maybe I've recently enjoyed some momentum on high level concepts (i.e. I produced software that fulfills a business need) and it'll take me a while to refocus my attention on low level implementations. Engaging one's brain carries some very variable overheads. If you just give me 5 minutes and watch me write every single line of code and comment about it while I'm doing it, then it's just not going to happen.

burgerdev 9y ago
You guys do realize that reversing a linked list is not 'solving a difficult programming puzzle'? Seeing the number of applicants that can't read lines from a file (in any given language), I'd say this question is adequate if you want to employ someone with programming experience.
- theprotocol 9y ago
  You're right about that particular exercise. I kind of used it to make a more general point.
beagle3 9y ago
Indeed. For the record, I let people take however much time they need, if they get stuck I ask them to discuss their approach, etc. I'm not looking for the solution (as parent said, it is a solved problem), I'm looking for evidence of problem solving skills. And you can demonstrate them, even for this question, without actually being able to write down a working solution. (I don't want to go into everything here, but one of the things I look for is people who consider the case of an empty list - critically thinking about special cases is an important trait) That said, work environment often has some kind of time constraint. If one can't solve any of the (simple, abstract, representative) problems that I pose within a 2hour time frame, it is possible that they are not a good match. And unfortunately, I rarely have the leisure to hire someone for a month to prove otherwise. [from a comment of yours below] > You're right about that particular exercise. I kind of used it to make a more general point. That may be true for others, but my interview questions are all of this mold: abstract, with a short and simple (but not trick-required-here) solution, close to (an abstract version of) a real world "business problem". I agree that technical interview questions (much like many aspects of life) put the wrong kind of stress on some and puts them at a disadvantage. But, and I always ask this[0], what alternative do you suggest? [0] The answers so far have been essentially either "no idea", "let me prove to you on my terms" (which, when broken down, is rarely economical for either side or at all possible), or "just trust me on this"; I find none of them satisfying.
- 9y ago

ThrowawayR2 9y ago

> When's the last time you ever did anything as low level as reversing a linked list? It's a topic covered in a sophomore-level data structures course over just a few days. If a college sophomore can pick it up that quickly (and "sophomoric" is a word for a reason), it should be no problem for a seasoned programmer to (re-)learn it in a couple of hours.

kstenerud 9y ago
How about in 10 minutes at a whiteboard while the interviewer waits patiently to judge you?
deleted 9y ago
[deleted]

sago 9y ago

> When's the last time you ever did anything as low level as reversing a linked list? It's a solved problem, and something an employee would NEVER do in your company I think that misses the point. A linked list is a simple data structure that needs little explanation, and yet uses indirection in a way that can get you into trouble. As such, it is a great toy problem to asses a person's ability to work with linked data. Reversing a list, is similarly, very simple to explain, and a quite rudimentary operation. So if I'm trying to asses basic ability to manipulate data in code, it seems much simpler than trying to give them a real-world linked data structure and have them do a real-world manipulation on it. The real problem is the assumption that this is a 'solved problem', i.e. that a) there is an one-true-way algorithm out there, and b) that is what the interviewer wants you to know (i.e. know in the sense of knowing a fact). That is true of too many interviewers, and that is the problem. I can imagine setting that as a question in an interview. And I wouldn't be interested in 'the algorithm', I'd want to see that someone could figure it out easily. If someone came in and clearly had just learnt it, it would tell me nothing. I would immediately ask them something else to take them out of their rote prep. But if someone came in and couldn't figure it out, why would I think they'd be any better on 'unsolved problems'? In terms of being able to manipulate data, it isn't much beyond Fizzbuzz. The 'it's a solved problem' attitude smacks of leftpad thinking to me.

kevan 9y ago
Exactly. As an interviewer I don't get any data if you have an algorithm memorized and throw it on the board. I'm trying to assess critical thinking and problem-solving skills, I've voted to hire many people who clearly had never seen the problem before, didn't get a working solution in the time we had, but demonstrated great problem-solving approach.
crdoconnor 9y ago
I almost exclusively give candidates realistic tasks (slightly modified real world tasks) and give them under realistic conditions (free access to google, candidate's own laptop preferably). It perplexes me. What do you gain by not doing that?
- 9y ago

temac 9y ago

Yep, you have the "far detached from real work" reaction. Plus, if you consider "you" (or an imaginary candidate you project yourself upon) risk not being able to answer it in 10 minutes because of such the high pressure it would put on you, then it basically means that you did not even try to answer it in your head, or that you were not able to. But this is the moral equivalent of asking a person who pretends to be a mathematician to do a 3 by 3 figures multiplication. It won't show much if they answer correctly (at least demonstrate a correct method to do it, never mind potential mistakes), but you can easily dismiss them if they fail. Now programming is a little bit different, because I admit there can be some positions where people can somehow contribute despite being incapable of lots of basic things. It depends on several factors, though, and even then I'm not sure the end result would ever be very solid. But I understand that in some contexts, such people would not be hired...

beagle3 9y ago

Wow, it appears my point was completely missed (and I was otherwise painted as a bigot), so let me try to explain better. > It's a solved problem, and something an employee would NEVER do in your company, let alone search for the optimal solution in 10 stressful minutes while you breathe down his neck. Actually, just a couple of weeks ago we had something almost equivalent, that involved chasing "pointers" through databases and files. It was for less than 1M cases, but still - any O(n^2) solution would have been infeasible (and an nlogn solution about 20 times slower than an O(n) solution; in this case, it was a one-off, and the difference would have been between 1hr of runtime and 1day of runtime). > When's the last time you ever did anything as low level as reversing a linked list? Please re-read what I wrote. I wrote, in fact, "you (almost) never need to reverse linked lists in practice". I also explained that it is an abstract version of a kind of thing that DOES happen often. > Major red flag. I don't mean to be rude, but this sentence comes off as very arrogant. Perhaps. For all you know, I'm a dog, but I'll say that I'm soon entering my 4th decade in the industry, I'm well respected, I've hired (and fired) tens of people through the years (and interviewed hundreds if not thousands); and I'm well respected among my peers for having very accurate evaluations of people's abilities. I do not aim to be politically correct. > Why? Because they're in a lower caste? If you can't handle direct feedback, you're a terrible manager. No, because I've just hired them, or just didn't hire them; either way, I think it is irresponsible to trust the statement of a person I don't actually know and who may either hold a grudge or want to please me right now. I meant to say "direct immediate feedback", which is perhaps better wording. After I know a person, I ask them (and usually get) the most direct and raw feedback I can get.

kstenerud 9y ago
> it was a one-off, and the difference would have been between 1hr of runtime and 1day of runtime). What's wrong with 1h vs 1d for a one-off thing? Your effective delivery time would be close enough to equivalent after all the administrative BS and customer expectations, and a naive approach piss simple to verify. If it was going to mean the difference between 1h and multiple days, here's what I'd do: - Fire up my trusty browser. - Navigate to google.com - Type in "reverse a linked list" - Evaluate all of the solutions I find and pick the best efficiency / verifiability match to solve the problem in a reasonable amount of time. Are you going to test that in an interview question? No, you're going to effectively "whiteboard" me, asking me to reinvent the wheel on the spot. And I'm going to resent you for it. > but I'll say that I'm soon entering my 4th decade in the industry, I'm well respected, I've hired (and fired) tens of people through the years (and interviewed hundreds if not thousands); and I'm well respected among my peers for having very accurate evaluations of people's abilities. I do not aim to be politically correct. And I'm in my third decade in the industry, all the respect, blah, blah, half a million lines of open source in the wild. So what? You can make the same mistakes over and over in any industry and never think to question if you're doing it wrong. This is ESPECIALLY problematic when it comes to people skills. > No, because I've just hired them, or just didn't hire them; either way, I think it is irresponsible to trust the statement of a person I don't actually know and who may either hold a grudge or want to please me right now. It's the PERFECT time to ask them, because it's fresh in their mind. A skilled interrogator can get information despite the subject's frame of mind. I'm actually surprised that you assume everyone you accept or reject is either going to be a sycophant or hold a grudge. You WANT them to talk while the frustrations they encountered are still fresh in their minds. That's the most raw feedback you'll ever get. You really do need to start treating them like human beings. Wanna know how I evaluated potential game devs in person? I asked them what dev environment they were most comfortable in, gave them a computer hooked up to the internet and a picture of a tweetie bird, and said "Make the bird jump. Use google to look shit up." Worked amazingly well.

joshjje 9y ago

Im not sure I agree with the premise that interview questions like that that may never come up in the job are useless. To me it doesnt matter. They are easily solvable and any competent programmer should be able to solve them. Of course I think more relevant questions are obviously better.

watwut 9y ago

> When's the last time you ever did anything as low level as reversing a linked list? It's a solved problem, and something an employee would NEVER do in your company, let alone search for the optimal solution in 10 stressful minutes while you breathe down his neck. I need occasional semi ad-hoc datastructures and manipulations like that. The requirement is never "reverse the list", but it is often something like "this api here needs input in opposite order and data happen to be in list". I would not see reverse the list as something specially unusual.