6 ms·

I remember when I was prepping for my Microsoft interview. There was so much lore online as to the types of questions they'd ask and how to prepare. I even foun

by csmatt 14y ago

I remember when I was prepping for my Microsoft interview. There was so much lore online as to the types of questions they'd ask and how to prepare. I even found 'How Would You Move Mount Fuji?' in the library and started reading through it. It was an absolute waste of time as I, fortunately, learned weeks before the interview. As an example, one of the questions I was asked was 'how would you write the C function strcmp() without using any libraries?' My gripe these days is that places I've interviewed with now that I have a few years of experience are still concerned about big-O notation and a lot of the more academic questions. I feel like I shouldn't have to go back to my college notes to prep for an interview for a job that I'd really be using my current experience for. I think it comes down to other developers not spending time really thinking about the quality of their interview questions. They just do a search for 'programming interview questions' and call it a day. My most recent interview was with Amazon. I was asked the dumb big-O runtime stuff as well as how I'd count all of the stars in the universe. It pissed me off, but I did like the question I was asked about how I'd design an elevator system and then asked how my solution would scale. That's not too far off from what I'd be doing, albeit in an abstract form.

rdtsc 14y ago
> and a lot of the more academic questions It is on purpose. A <bigcompany> recruiter confessed. He said they are specifically targeting recent grads. So plenty of questions are of that type. I guess they want to indoctrinate and take advantage of them while they are "fresh". > did like the question I was asked about how I'd design an elevator system and then asked how my solution would scale. That's not too far off from what I'd be doing, albeit in an abstract form. That would piss me off though too. "So does Amazon write algorithms for its elevators?". Why not just simplify a problem they solve. "So you have key value storage and you want to make it distributed". Why even talk about elevators?
- saosebastiao 14y ago
  Actually, yes...they do. I work in a building with an elevator control system designed by an internal engineer. More importantly, the elevator control system uses mathematical expertise that is normally used solving variants of the multi-commodity flow problem, used extensively in the Supply Chain.
  - rdtsc 14y ago
    > Actually, yes...they do. I work in a building with an elevator control system designed by an internal engineer. Well then that makes a good interview question then!
  - reledi 14y ago
    Heh, that's pretty cool. How does it compare to the average elevator?
    - sib 14y ago
      When load is not particularly high, it works well (seemingly efficient for passengers and in energy consumption). When load gets high (think ~noon), it tends to perform pretty badly in terms of latency.
    - saosebastiao 14y ago
      Sib has it about right. It is an NP complete problem, and I'm pretty sure the solution is using a Heuristic, but it does seem to be pretty suboptimal during lunch time. Then again, maybe it just seems worse because you wait longer as a tradeoff to having a faster ride to your floor.
andrewvc 14y ago
I generally agree, most logic questions are useless, but Big-O notation I use every day. Programmers who don't understand the performance difference between Array#include? and Set#include? in ruby are dangerous!
- randomdata 14y ago
  I'm curious to know where you use the notation in daily programming. In code comments? Discussions with other developers? Other documentation? I use the spirt of Big-O almost daily, but do the actual calculations rarely, and basically never use the notation. With some experience, you quickly get an intuitive feel for execution time, which is good enough in most cases.
  - kamaal 14y ago
    Actually using something like a math notation to solve a programming problem is asking for too much. What are those general problems which can't be solved by standard libraries, frameworks and IDE's these days? And even if you are facing problems that mandate you to roll out your stuff how much of that requires these math tricks. Given all this, if you truly want to hire a math geek to get some magic done. I guess you are looking at a very small pool of people to hire from and it should hardly be a problem to hire one.
    - to3m 14y ago
      Big-O notation is hardly "math geek" stuff. I'd not call this comment ridiculous, because I might have misunderstood it, but catch me in my cups and ask me for my true opinion and maybe I'd say that. Big-O notation is pretty basic, and very useful. Combined with a memorized table of powers of two (you don't need all of them - I know up to 2^20, and this has proven sufficient - just enough so you can guess log N for a given value) you have a good chance at being able to make quick calculations about time and space requirements for things. Which, since we don't have infinitely fast computers with infinite amounts of memory, often comes in handy.
      - 14y ago
3pt14159 14y ago
"What is the big O time of heap sort?" vs "Would you mind writing a function that returns true if any two numbers in the list sum to zero? For example, it would return false for [2,3,5] and true for [-3,5,3]" Are completely different questions. The first is useless: It tests if someone remembers how a heap sort works, and whether or not they use the term "worst case" in the answer. The second one is much better. Some could sort the list, (nlogn time, constant memory) then walk through it. They could use a hash table (idealy n time, assuming no collisions, but more memory). You also get to see if their solution handles the 0 case. If they answer it very quickly, you can move on to the three sum problem. If they recognize the question from university or something you can do a different one. If someone doesn't know the big-O time of iterating through a list of integers once for every integer, then I seriously doubt their dedication to the field of software. This is not some pie in the sky doubt, it is of legitimate concern whether someone knows how to properly approach a problem of this nature with the right data structures, code, and communication. Good interviewers put the interviewee at complete ease before they bring out the technical questions. From an economics point of view, it is better to hire the person that is in all other ways identical, yet interviews poorly, since they are less likely to want to leave.
- pm90 14y ago
  Very good illustration, I must say. I strongly disagreed with the GP's rant about knowing O-notation, but I realized he might have faced the first type of questions a lot (e.g tell me the O-complexity of X algorithm). My experience with Amazon was actually the opposite, but I might have been lucky. All the interviewers were very friendly and started from simple questions and went on to more complex ones. Never a "do you know concept a from language Y". In fact, one of them worked with me through the solution to a pretty tricky problem, and when we were done, he actually took a picture of my solution on the whiteboard! So yeah, it was fun :)
  - cwarrior 14y ago
    Were you given an offer by Amazon?
  - saryant 14y ago
southphillyman 14y ago
Yea this is where I'm at with it. If I walk into an interview and the first question is what is the difference between an abstract class and an interface my interest in the interview is probably going to decrease exponentially. How about asking me about my design approach to a specific problem, what frameworks have I try when presented with a specific problem and my thoughts on it, or what I'm currently learning. I get why they do it but at a certain level it's almost a sign of disrespect to be asked to fizzbuzz if you can verify I've been working at reputable companies for the last x yrs. Let's have a more nuanced discussion about technology so that you can confirm that I didn't just cram certification questions over the weekend and I can get a gauge on the type of problems I may have to tackle on the job.
- NateDad 14y ago
  You assume people working at programming jobs for years on end have a clue... that's not always true. I've worked with people who couldn't do fizzbuzz, or describe the difference between an interface and an abstract class, or any other basic programming stuff. If they throw you an easy pitch, knock it out of the park and they'll ask you something more difficult afterward.
  - andrewaylett 14y ago
    This is precisely right: I ask people questions like the difference between an interface and an abstract class as a gauge, because I've had so many people answer them really badly. The question wouldn't normally come out of the blue, though, but as a follow-up from part of a design exercise where they would have just used one or the other in their design, and as part of finding out whether they could justify their choice.
thedufer 14y ago
> are still concerned about big-O notation Time complexity is important, and hiring someone who doesn't think so is dangerous. That said, it's important to ask about an algorithm you've already discussed. Asking "what's the big-O of <generic algorithm>" also tests for whether you remember the specifics of that algorithm, which isn't terribly useful.
danielweber 14y ago
There are jobs where algorithms matter. Where someone picking the wrong data structure or algorithm can completely fuck up the problem, or where the company's secret sauce is doing something much faster than their competitors are doing it.

by csmatt 14y ago

rdtsc 14y ago

> and a lot of the more academic questions It is on purpose. A <bigcompany> recruiter confessed. He said they are specifically targeting recent grads. So plenty of questions are of that type. I guess they want to indoctrinate and take advantage of them while they are "fresh". > did like the question I was asked about how I'd design an elevator system and then asked how my solution would scale. That's not too far off from what I'd be doing, albeit in an abstract form. That would piss me off though too. "So does Amazon write algorithms for its elevators?". Why not just simplify a problem they solve. "So you have key value storage and you want to make it distributed". Why even talk about elevators?

saosebastiao 14y ago
Actually, yes...they do. I work in a building with an elevator control system designed by an internal engineer. More importantly, the elevator control system uses mathematical expertise that is normally used solving variants of the multi-commodity flow problem, used extensively in the Supply Chain.
- rdtsc 14y ago
  > Actually, yes...they do. I work in a building with an elevator control system designed by an internal engineer. Well then that makes a good interview question then!
- reledi 14y ago
  Heh, that's pretty cool. How does it compare to the average elevator?
  - sib 14y ago
    When load is not particularly high, it works well (seemingly efficient for passengers and in energy consumption). When load gets high (think ~noon), it tends to perform pretty badly in terms of latency.
  - saosebastiao 14y ago
    Sib has it about right. It is an NP complete problem, and I'm pretty sure the solution is using a Heuristic, but it does seem to be pretty suboptimal during lunch time. Then again, maybe it just seems worse because you wait longer as a tradeoff to having a faster ride to your floor.

andrewvc 14y ago

I generally agree, most logic questions are useless, but Big-O notation I use every day. Programmers who don't understand the performance difference between Array#include? and Set#include? in ruby are dangerous!

randomdata 14y ago
I'm curious to know where you use the notation in daily programming. In code comments? Discussions with other developers? Other documentation? I use the spirt of Big-O almost daily, but do the actual calculations rarely, and basically never use the notation. With some experience, you quickly get an intuitive feel for execution time, which is good enough in most cases.
- kamaal 14y ago
  Actually using something like a math notation to solve a programming problem is asking for too much. What are those general problems which can't be solved by standard libraries, frameworks and IDE's these days? And even if you are facing problems that mandate you to roll out your stuff how much of that requires these math tricks. Given all this, if you truly want to hire a math geek to get some magic done. I guess you are looking at a very small pool of people to hire from and it should hardly be a problem to hire one.
  - to3m 14y ago
    Big-O notation is hardly "math geek" stuff. I'd not call this comment ridiculous, because I might have misunderstood it, but catch me in my cups and ask me for my true opinion and maybe I'd say that. Big-O notation is pretty basic, and very useful. Combined with a memorized table of powers of two (you don't need all of them - I know up to 2^20, and this has proven sufficient - just enough so you can guess log N for a given value) you have a good chance at being able to make quick calculations about time and space requirements for things. Which, since we don't have infinitely fast computers with infinite amounts of memory, often comes in handy.
    - 14y ago

3pt14159 14y ago

"What is the big O time of heap sort?" vs "Would you mind writing a function that returns true if any two numbers in the list sum to zero? For example, it would return false for [2,3,5] and true for [-3,5,3]" Are completely different questions. The first is useless: It tests if someone remembers how a heap sort works, and whether or not they use the term "worst case" in the answer. The second one is much better. Some could sort the list, (nlogn time, constant memory) then walk through it. They could use a hash table (idealy n time, assuming no collisions, but more memory). You also get to see if their solution handles the 0 case. If they answer it very quickly, you can move on to the three sum problem. If they recognize the question from university or something you can do a different one. If someone doesn't know the big-O time of iterating through a list of integers once for every integer, then I seriously doubt their dedication to the field of software. This is not some pie in the sky doubt, it is of legitimate concern whether someone knows how to properly approach a problem of this nature with the right data structures, code, and communication. Good interviewers put the interviewee at complete ease before they bring out the technical questions. From an economics point of view, it is better to hire the person that is in all other ways identical, yet interviews poorly, since they are less likely to want to leave.

pm90 14y ago
Very good illustration, I must say. I strongly disagreed with the GP's rant about knowing O-notation, but I realized he might have faced the first type of questions a lot (e.g tell me the O-complexity of X algorithm). My experience with Amazon was actually the opposite, but I might have been lucky. All the interviewers were very friendly and started from simple questions and went on to more complex ones. Never a "do you know concept a from language Y". In fact, one of them worked with me through the solution to a pretty tricky problem, and when we were done, he actually took a picture of my solution on the whiteboard! So yeah, it was fun :)
- cwarrior 14y ago
  Were you given an offer by Amazon?
- saryant 14y ago

southphillyman 14y ago

Yea this is where I'm at with it. If I walk into an interview and the first question is what is the difference between an abstract class and an interface my interest in the interview is probably going to decrease exponentially. How about asking me about my design approach to a specific problem, what frameworks have I try when presented with a specific problem and my thoughts on it, or what I'm currently learning. I get why they do it but at a certain level it's almost a sign of disrespect to be asked to fizzbuzz if you can verify I've been working at reputable companies for the last x yrs. Let's have a more nuanced discussion about technology so that you can confirm that I didn't just cram certification questions over the weekend and I can get a gauge on the type of problems I may have to tackle on the job.

NateDad 14y ago
You assume people working at programming jobs for years on end have a clue... that's not always true. I've worked with people who couldn't do fizzbuzz, or describe the difference between an interface and an abstract class, or any other basic programming stuff. If they throw you an easy pitch, knock it out of the park and they'll ask you something more difficult afterward.
- andrewaylett 14y ago
  This is precisely right: I ask people questions like the difference between an interface and an abstract class as a gauge, because I've had so many people answer them really badly. The question wouldn't normally come out of the blue, though, but as a follow-up from part of a design exercise where they would have just used one or the other in their design, and as part of finding out whether they could justify their choice.

thedufer 14y ago

> are still concerned about big-O notation Time complexity is important, and hiring someone who doesn't think so is dangerous. That said, it's important to ask about an algorithm you've already discussed. Asking "what's the big-O of <generic algorithm>" also tests for whether you remember the specifics of that algorithm, which isn't terribly useful.

danielweber 14y ago

There are jobs where algorithms matter. Where someone picking the wrong data structure or algorithm can completely fuck up the problem, or where the company's secret sauce is doing something much faster than their competitors are doing it.