6 ms·

Most candidates cannot solve this interview problem

17 points by raymondh 6y ago

sammy533 6y ago
This is trivial for me to solve, sitting here at my computer. Would I be a me to solve it on a whiteboard in front of a group of interviewers? Maybe not. The stress and anxiety may get the best of me.
- zzo38computer 6y ago
  I agree with you; it is easy solving sitting at the computer, but in front of a group of interviewers might be stressful like that. The method to solve it depends on the programming language. In this case, I would use Haskell; however, this would likely be a part of a larger program, and in that case the programming language that the larger program is written in would be used instead.
enjoyyourlife 6y ago
Clickbait title
- raymondh 6y ago
  Given that those exact words are the first line of the tweet and that it is almost the entire point of the post, what alternative title would have been better?
  - enjoyyourlife 6y ago
    Something like "Most candidates that I interviewed cannot write a function that does run-length encoding"
GiorgioG 6y ago
Can I solve it? Yes. Is it a reflection of how well I can do my job? No. Will I be solving these kinds of problems at this job? Very unlikely. This is a massive waste of everyone's time and tells you nothing about the candidate's ability to do the job. Try again.
- d0mine 6y ago
  If most candidates cannot solve it in 25 minutes (while being a simple task), then it is a valid test [(c, sum(1 for _ in same)) for c, same in itertools.groupby(s)]
  - chrisandchris 6y ago
    Does this a actually solve it? It should only sum when the character next to is the same as the previous. a is counted twice: ([a, 3], ... [a, 1]) While I agree that such interview questions are bad, they also give the interviewer a view on how the interviewee attempts to solve a problem. Edit: typo
    - d0mine 6y ago
      Yes, it does solve it. It produces the expected output (`a` should occur twice) Here's solution that doesn't use itertools.groupby() https://docs.python.org/3/library/itertools.html?highlight=itertools#itertools.groupby https://docs.python.org/3/library/itertools.html?highlight=i... : result = [] prev, count = None, 0 for c in s+"\0": # note: assuming "\0" can't be in `s` if c != prev: # starting new sequence if count: # save count for old sequence result.append((prev, count)) prev, count = c, 1 # reset count else: # continuation of old sequence count += 1
      - chrisandchris 6y ago
        Ok, thanks. I don‘t speak enough python to understand that it solves the issue.
  - d0mine 6y ago
    Please do comment if you downvote a correct solution.
jwilber 6y ago
This is seemingly the software equivalent of those trivial order of operations problems you see reposted over and over again on Facebook/Twitter. I can never tell if the objective is to give novel solutions to the problem or to just publicly show that you can solve it. In any case, I always chuckle when I see how some of those in the comments can reply so smugly to others.
IgorBog61650384 6y ago
I think this approach might backfire: If purpose of the question is to test the candidate's knowledge of common libraries, then it probably is way to easy to be indicative, this kind of knowledge should be tested for something the candidate can't find by googling for 5 minutes. If the purpose is to test algorithm design, its also way to basic.
- Someone 6y ago
  Apparently, FizzBuzz (https://imranontech.com/2007/01/24/using-fizzbuzz-to-find-developers-who-grok-coding/ https://imranontech.com/2007/01/24/using-fizzbuzz-to-find-de.... A nice page about it: https://www.tomdalling.com/blog/software-design/fizzbuzz-in-too-much-detail/ https://www.tomdalling.com/blog/software-design/fizzbuzz-in-...) is a useful test to weed out bad programmers. If so, this can, too.
- fr2null 6y ago
  While most of the comments on the Twitter thread use fancy functions from common libraries, you should be able to solve this problem without the need for googling and without those fancy functions. While I agree that this is way to basic to test AD skills, if it's really true that there is a sizable percentage of people that is unable to solve this problem, this might be a good way to weed those out, before starting with the 'real' questions.
Supermancho 6y ago
Notably, none of the answers given (despite being clever solutions to get the data) output the exact format requested. [("..",..),...]
- pensatoio 6y ago
  If I gave a correct answers to a question like this and they responded as you suggest, I’d leave immediately. The purpose of this line of questioning is to weed out incompetent programmers, not be petty. If the latter is a priority, then working with them will undoubtedly be a trial.
- pcthrowaway 6y ago
  possibly because it's much harder (maybe impossible?) to do in languages that don't have native tuples, which appear to be the ask. The input string is quoted, so the output appears to be an array (not a string type). My stab at it in Javascript resulted in: function collapse(a) { collapsedArray = []; for (let i=0; i<a.length; i++) { let count = 1; let currentchar = a[i]; while (i+1 < a.length && a[i+1] == currentchar) { i++; count++; } collapsedArray.push([a[i], count]); } return (collapsedArray); } console.log(JSON.stringify(collapse("aabbcdde"))); This outputs `[["a",2],["b",2],["c",1],["d",2],["e",1]]`. Without native tuples in Javascript (or JSON), I could construct a string which replaces the inner brackets with parens, but that would be pretty contrived, as the output requested isn't quoted.
  - Supermancho 6y ago
    > the output requested isn't quoted. Input: "aaaabbbcca" Output: [("a", 4), ("b", 3), ("c", 2), ("a", 1)] The input and output is explicit. The interpretation is a talking point. Serialization into parens is not native for most? scripting languages. Creating a string would probably be most efficient for the output format, for sure. It's important to remember that interview questions are not just about the algorithm (for which this is trivial) but the requirements. Asking if the double quotes are representing strings (and what kind of strings for some languages) is part of the natural back-and-forth of an interview.
hyperrealgopher 6y ago
Hello, Hacker News! I'm new to the community. I just saw this and thought it'd be fun to solve in Haskell. The first solution I thought of was done in under a couple minutes. The second solution (I wanted to implement `group` myself) took a lot longer because I messed up a pattern match! https://gist.github.com/hyperrealgopher/19730725804ba8825d50d96f75b88a96 https://gist.github.com/hyperrealgopher/19730725804ba8825d50...
- solresol 6y ago
  > module Main where > input = "aaaabbbcca" > r :: String -> (Char,Int) -> [(String, Int)] > r [] (c,n) = [([c],n)] > r (x:xs) (c,n) > | c == x = r xs (c,n+1) > | otherwise = (([c],n): r xs (x,1)) > main = putStrLn (show (r (tail input) (head input, 1) )) 4 minutes 42 seconds. And no, I don't write code like this normally, but I guess this is me when I'm under time pressure... anyway, I could refactor it nicely afterwards in the 25 minutes allocated.
  - deleted 6y ago
    [deleted]
  - hyperrealgopher 6y ago
    Great solution that avoids using any functions that do the heavy lifting for you! Thanks for showing!
- zzo38computer 6y ago
  My own first idea was actually similar to yours, although I wrote: map (head &&& length) . group (Also, it took me only a few seconds, because it just seemed obvious to me, even though Haskell is not the programming language I normally use for my projects, but it seems the right thing for this.)
  - deleted 6y ago
    [deleted]
  - hyperrealgopher 6y ago
xupybd 6y ago
If nothing else this makes me feel better about my own abilities. Unfortunately I find it's not my ability to solve tricky puzzles but my ability to solve business problems in minimal time. Often the hard part is not the algorithm design but extracting the requirements that will bring the most benefit to the business.

17 points by raymondh 6y ago

This is trivial for me to solve, sitting here at my computer. Would I be a me to solve it on a whiteboard in front of a group of interviewers? Maybe not. The stress and anxiety may get the best of me.

zzo38computer 6y ago
I agree with you; it is easy solving sitting at the computer, but in front of a group of interviewers might be stressful like that. The method to solve it depends on the programming language. In this case, I would use Haskell; however, this would likely be a part of a larger program, and in that case the programming language that the larger program is written in would be used instead.

enjoyyourlife 6y ago

Clickbait title

raymondh 6y ago
Given that those exact words are the first line of the tweet and that it is almost the entire point of the post, what alternative title would have been better?
- enjoyyourlife 6y ago
  Something like "Most candidates that I interviewed cannot write a function that does run-length encoding"

GiorgioG 6y ago

Can I solve it? Yes. Is it a reflection of how well I can do my job? No. Will I be solving these kinds of problems at this job? Very unlikely. This is a massive waste of everyone's time and tells you nothing about the candidate's ability to do the job. Try again.

d0mine 6y ago
If most candidates cannot solve it in 25 minutes (while being a simple task), then it is a valid test [(c, sum(1 for _ in same)) for c, same in itertools.groupby(s)]
- chrisandchris 6y ago
  Does this a actually solve it? It should only sum when the character next to is the same as the previous. a is counted twice: ([a, 3], ... [a, 1]) While I agree that such interview questions are bad, they also give the interviewer a view on how the interviewee attempts to solve a problem. Edit: typo
  - d0mine 6y ago
    Yes, it does solve it. It produces the expected output (`a` should occur twice) Here's solution that doesn't use itertools.groupby() https://docs.python.org/3/library/itertools.html?highlight=itertools#itertools.groupby https://docs.python.org/3/library/itertools.html?highlight=i... : result = [] prev, count = None, 0 for c in s+"\0": # note: assuming "\0" can't be in `s` if c != prev: # starting new sequence if count: # save count for old sequence result.append((prev, count)) prev, count = c, 1 # reset count else: # continuation of old sequence count += 1
    - chrisandchris 6y ago
      Ok, thanks. I don‘t speak enough python to understand that it solves the issue.
- d0mine 6y ago
  Please do comment if you downvote a correct solution.

jwilber 6y ago

This is seemingly the software equivalent of those trivial order of operations problems you see reposted over and over again on Facebook/Twitter. I can never tell if the objective is to give novel solutions to the problem or to just publicly show that you can solve it. In any case, I always chuckle when I see how some of those in the comments can reply so smugly to others.

IgorBog61650384 6y ago

I think this approach might backfire: If purpose of the question is to test the candidate's knowledge of common libraries, then it probably is way to easy to be indicative, this kind of knowledge should be tested for something the candidate can't find by googling for 5 minutes. If the purpose is to test algorithm design, its also way to basic.

Someone 6y ago
Apparently, FizzBuzz (https://imranontech.com/2007/01/24/using-fizzbuzz-to-find-developers-who-grok-coding/ https://imranontech.com/2007/01/24/using-fizzbuzz-to-find-de.... A nice page about it: https://www.tomdalling.com/blog/software-design/fizzbuzz-in-too-much-detail/ https://www.tomdalling.com/blog/software-design/fizzbuzz-in-...) is a useful test to weed out bad programmers. If so, this can, too.
fr2null 6y ago
While most of the comments on the Twitter thread use fancy functions from common libraries, you should be able to solve this problem without the need for googling and without those fancy functions. While I agree that this is way to basic to test AD skills, if it's really true that there is a sizable percentage of people that is unable to solve this problem, this might be a good way to weed those out, before starting with the 'real' questions.

Supermancho 6y ago

Notably, none of the answers given (despite being clever solutions to get the data) output the exact format requested. [("..",..),...]

pensatoio 6y ago
If I gave a correct answers to a question like this and they responded as you suggest, I’d leave immediately. The purpose of this line of questioning is to weed out incompetent programmers, not be petty. If the latter is a priority, then working with them will undoubtedly be a trial.
pcthrowaway 6y ago
possibly because it's much harder (maybe impossible?) to do in languages that don't have native tuples, which appear to be the ask. The input string is quoted, so the output appears to be an array (not a string type). My stab at it in Javascript resulted in: function collapse(a) { collapsedArray = []; for (let i=0; i<a.length; i++) { let count = 1; let currentchar = a[i]; while (i+1 < a.length && a[i+1] == currentchar) { i++; count++; } collapsedArray.push([a[i], count]); } return (collapsedArray); } console.log(JSON.stringify(collapse("aabbcdde"))); This outputs `[["a",2],["b",2],["c",1],["d",2],["e",1]]`. Without native tuples in Javascript (or JSON), I could construct a string which replaces the inner brackets with parens, but that would be pretty contrived, as the output requested isn't quoted.
- Supermancho 6y ago
  > the output requested isn't quoted. Input: "aaaabbbcca" Output: [("a", 4), ("b", 3), ("c", 2), ("a", 1)] The input and output is explicit. The interpretation is a talking point. Serialization into parens is not native for most? scripting languages. Creating a string would probably be most efficient for the output format, for sure. It's important to remember that interview questions are not just about the algorithm (for which this is trivial) but the requirements. Asking if the double quotes are representing strings (and what kind of strings for some languages) is part of the natural back-and-forth of an interview.

hyperrealgopher 6y ago

Hello, Hacker News! I'm new to the community. I just saw this and thought it'd be fun to solve in Haskell. The first solution I thought of was done in under a couple minutes. The second solution (I wanted to implement `group` myself) took a lot longer because I messed up a pattern match! https://gist.github.com/hyperrealgopher/19730725804ba8825d50d96f75b88a96 https://gist.github.com/hyperrealgopher/19730725804ba8825d50...

solresol 6y ago
> module Main where > input = "aaaabbbcca" > r :: String -> (Char,Int) -> [(String, Int)] > r [] (c,n) = [([c],n)] > r (x:xs) (c,n) > | c == x = r xs (c,n+1) > | otherwise = (([c],n): r xs (x,1)) > main = putStrLn (show (r (tail input) (head input, 1) )) 4 minutes 42 seconds. And no, I don't write code like this normally, but I guess this is me when I'm under time pressure... anyway, I could refactor it nicely afterwards in the 25 minutes allocated.
- deleted 6y ago
  [deleted]
- hyperrealgopher 6y ago
  Great solution that avoids using any functions that do the heavy lifting for you! Thanks for showing!
zzo38computer 6y ago
My own first idea was actually similar to yours, although I wrote: map (head &&& length) . group (Also, it took me only a few seconds, because it just seemed obvious to me, even though Haskell is not the programming language I normally use for my projects, but it seems the right thing for this.)
- deleted 6y ago
  [deleted]
- hyperrealgopher 6y ago

xupybd 6y ago

If nothing else this makes me feel better about my own abilities. Unfortunately I find it's not my ability to solve tricky puzzles but my ability to solve business problems in minimal time. Often the hard part is not the algorithm design but extracting the requirements that will bring the most benefit to the business.