6 ms·

> 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 co

by 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?
- poikniok 9y ago
  Research mathematicians are made in large part in the process of taking classes with tests for several years. Why don't they just ask the students to write papers if that is the end goal?
  - posterboy 9y ago
    The tests, homeworks etc. are largely production of papers, on a lower scale perhaps, and interspersed with notes, but as far as I know not multiple choice nor mere reciting definitions or trivial algorithmic execution as most of the stuff is not concrete. I'm not a maths student so my maths tests are of the latter variant.
- ethan_g 9y ago
  Whether you can give real-world questions depends a lot on the domain. If you're using popular open-source tools, you may be able to test a candidate on the ability to complete standard tasks with them. But what if you're using tons of proprietary software and working in a specialized domain where you expect people to learn on the job? That was the case where I used to work (quant finance). We need programming questions that assess candidate's general ability rather than anything domain-specific. The linked-list question is a perfectly fair non-domain-specific question.
  - crdoconnor 9y ago
    >But what if you're using tons of proprietary software and working in a specialized domain where you expect people to learn on the job? Then use it in the test! If you're judging people on how well they pick up proprietary software, give to them and make them do something with it. My tests usually involve giving the candidate exposure to some software/module or other which they were not previously familiar and I judge them on how well they can work with it, applying general programming knowledge they will actually use day to do in the process.
    - joshuamorton 9y ago
vpeters25 9y ago
> 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. These "solved problems" are the result of countless hours of research by computer science experts with masters and Ph.D degrees. For those of you who studied computer science in college, you likely had lectures where the teacher or TA walked you through the process of resolving each of these algorithms. Unless you are hiring for companies like Netflix, Cloudflare, Google, etc. where you basically need to invent new fields of research in computer science, expecting a programmer to "come up" with the same solution in 10 minutes a team of CS experts solved after many hours of research might be a little unrealistic.
- sago 9y ago
  > These "solved problems" are the result of countless hours of research by computer science experts with masters and Ph.D degrees. We're talking about reversing a linked list, right? This is the second time I've had this kind of surreal conversation on HN (the first was summing a list of integers), and I confess I am completely baffled. We are talking about reversing a linked list. I absolutely expect somebody with a even minimal programming competence to be able to perform simple manipulations on interconnected data. And I can't imagine a much simpler manipulation, taking into account the connections, than that. Knowing the difference between a problem that you can solve intuitively, And one that requires hours of PhD research, is also a good skill to have.
  - joshjje 9y ago
    Yeah, dont worry about him. I fully agree with everything you are saying.
  - kstenerud 9y ago
    Yes, it's only a linked list, and reversing it is trivial. The problem comes with the inevitable "OK, now how would you make it more space/time efficient?" question. I've had it countless times, and it's always infuriating because the answer is out there, on google, written by some PHD ages ago. The interviewer himself has read it, which is why he knows, and yet now he expects me to come up with something comparable in a "clean room" situation, usually involving a white board. Really, those kinds of questions such as algorithm optimization only test your ability to come up with creative solutions in a stressful and time constrained situation. And even then you're not testing that because even the best of us will experience temporary brain paralysis in stressful situations, so you're actually just testing for luck. And if that's what the working environment is like, fine so long as the candidate knows it's always like that and accepts those conditions (I wouldn't). But if that's NOT what the working environment is like, why are you even testing for it?
clarry 9y ago
> But if someone came in and couldn't figure it out, why would I think they'd be any better on 'unsolved problems'? It's an easy problem for sure, and I yet I could imagine many a competent programmer to lock up for reasons that have nothing to do with the problem and everything to do with the situation and sense of pressure they might experience during it.
- concede_pluto 9y ago
  I haven't worked on shrinkwrap software since 2006. For the last eleven years, every developer role I've had required me to be on call and troubleshoot when prod fails in the middle of the night. If you can't be relied on to do that, there are only certain teams that can use you, and I don't conduct their interviews.
  - sobani 9y ago
    The stress from a interview is vastly different from the pressure of fixing a prod issue. It's like saying standup comedy prepares you for 3AM calls.

by sago 9y ago

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?

poikniok 9y ago
Research mathematicians are made in large part in the process of taking classes with tests for several years. Why don't they just ask the students to write papers if that is the end goal?
- posterboy 9y ago
  The tests, homeworks etc. are largely production of papers, on a lower scale perhaps, and interspersed with notes, but as far as I know not multiple choice nor mere reciting definitions or trivial algorithmic execution as most of the stuff is not concrete. I'm not a maths student so my maths tests are of the latter variant.
ethan_g 9y ago
Whether you can give real-world questions depends a lot on the domain. If you're using popular open-source tools, you may be able to test a candidate on the ability to complete standard tasks with them. But what if you're using tons of proprietary software and working in a specialized domain where you expect people to learn on the job? That was the case where I used to work (quant finance). We need programming questions that assess candidate's general ability rather than anything domain-specific. The linked-list question is a perfectly fair non-domain-specific question.
- crdoconnor 9y ago
  >But what if you're using tons of proprietary software and working in a specialized domain where you expect people to learn on the job? Then use it in the test! If you're judging people on how well they pick up proprietary software, give to them and make them do something with it. My tests usually involve giving the candidate exposure to some software/module or other which they were not previously familiar and I judge them on how well they can work with it, applying general programming knowledge they will actually use day to do in the process.
  - joshuamorton 9y ago

vpeters25 9y ago

> 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. These "solved problems" are the result of countless hours of research by computer science experts with masters and Ph.D degrees. For those of you who studied computer science in college, you likely had lectures where the teacher or TA walked you through the process of resolving each of these algorithms. Unless you are hiring for companies like Netflix, Cloudflare, Google, etc. where you basically need to invent new fields of research in computer science, expecting a programmer to "come up" with the same solution in 10 minutes a team of CS experts solved after many hours of research might be a little unrealistic.

sago 9y ago
> These "solved problems" are the result of countless hours of research by computer science experts with masters and Ph.D degrees. We're talking about reversing a linked list, right? This is the second time I've had this kind of surreal conversation on HN (the first was summing a list of integers), and I confess I am completely baffled. We are talking about reversing a linked list. I absolutely expect somebody with a even minimal programming competence to be able to perform simple manipulations on interconnected data. And I can't imagine a much simpler manipulation, taking into account the connections, than that. Knowing the difference between a problem that you can solve intuitively, And one that requires hours of PhD research, is also a good skill to have.
- joshjje 9y ago
  Yeah, dont worry about him. I fully agree with everything you are saying.
- kstenerud 9y ago
  Yes, it's only a linked list, and reversing it is trivial. The problem comes with the inevitable "OK, now how would you make it more space/time efficient?" question. I've had it countless times, and it's always infuriating because the answer is out there, on google, written by some PHD ages ago. The interviewer himself has read it, which is why he knows, and yet now he expects me to come up with something comparable in a "clean room" situation, usually involving a white board. Really, those kinds of questions such as algorithm optimization only test your ability to come up with creative solutions in a stressful and time constrained situation. And even then you're not testing that because even the best of us will experience temporary brain paralysis in stressful situations, so you're actually just testing for luck. And if that's what the working environment is like, fine so long as the candidate knows it's always like that and accepts those conditions (I wouldn't). But if that's NOT what the working environment is like, why are you even testing for it?

clarry 9y ago

> But if someone came in and couldn't figure it out, why would I think they'd be any better on 'unsolved problems'? It's an easy problem for sure, and I yet I could imagine many a competent programmer to lock up for reasons that have nothing to do with the problem and everything to do with the situation and sense of pressure they might experience during it.

concede_pluto 9y ago
I haven't worked on shrinkwrap software since 2006. For the last eleven years, every developer role I've had required me to be on call and troubleshoot when prod fails in the middle of the night. If you can't be relied on to do that, there are only certain teams that can use you, and I don't conduct their interviews.
- sobani 9y ago
  The stress from a interview is vastly different from the pressure of fixing a prod issue. It's like saying standup comedy prepares you for 3AM calls.