4 ms·

> They lie about being able to code. If someone successfully works shipping code but can't reverse a linked list, does that mean they're lying about being able

by rr808 5y ago

> They lie about being able to code. If someone successfully works shipping code but can't reverse a linked list, does that mean they're lying about being able to code? I've seen way to many jobs that test for expert level skills for a job that is just to add small enhancements.

ThrowawayR2 5y ago
> "If someone successfully works shipping code but can't reverse a linked list, does that mean they're lying about being able to code?" Obviously yes? That's a basic assignment for a data structure class given to freshmen and sophomores. One would expect that a "senior" developer (degreed or self-taught) would be better than a college sophomore. At the FAANG level, it would be a phone screen question and a softball one at that.
- mooreds 5y ago
  I've held several senior developer positions and I'd have to study up on how to reverse a linked list. (Other than the obvious answer: "use a library/built-in function to do it", which would probably would not be a satisfactory answer.) I think the problem is that there are over a dozen different kinds of "seniority" but we collapse them all into one term. I got so frustrated I wrote a blog post about it: https://www.mooreds.com/wordpress/archives/2812 https://www.mooreds.com/wordpress/archives/2812
  - kragen 5y ago
    It might depend on what the measure of "senior developer" is. There are junior-developer positions where nobody could perform adequately without being comfortable manipulate linked data structures (Linux kernel development, maybe, or working on a garbage collector or JIT compiler or the Postgres query optimizer) but senior developers on those teams probably don't know a tenth of what you know about SQL. Also there are ancillary skills that make the problem much less difficult, so if you can't solve it, you don't have them. Joel Spolsky famously said that nobody can reverse a linked list without drawing diagrams on paper, and that's probably true if you're doing it imperatively in C. But it's in the category of "problems that become much simpler with functional styles of programming." The following took me 5 minutes, most of which was struggling with the syntax of OCaml that I'd forgotten: $ ocaml OCaml version 4.08.1 # type 'a list = Cons of ('a * 'a list) | Nil;; type 'a list = Cons of ('a * 'a list) | Nil # Cons(3, Cons(41, Nil));; - : int list = Cons (3, Cons (41, Nil)) # let reverse lst = let rec rev xs ys = match xs with Nil -> ys | Cons(x, xs') -> rev xs' (Cons(x, ys)) in rev lst Nil ;; val reverse : 'a list -> 'a list = <fun> # reverse(Cons(3, Cons(41, Nil)));; - : int list = Cons (41, Cons (3, Nil)) The full session with all my dumb errors: $ ocaml OCaml version 4.08.1 # type 'a list = Cons of ('a * 'a list) | Nil;; type 'a list = Cons of ('a * 'a list) | Nil # Cons 3 (Cons 41 Nil) ;; Error: Syntax error # Cons(3, Cons(41, Nil));; - : int list = Cons (3, Cons (41, Nil)) # let reverse lst = let rec rev xs ys = match xs with Nil -> ys | Cons(x, xs') -> rev xs' Cons(x, ys) ;; Error: Syntax error # let reverse lst = let rec rev xs ys = match xs with Nil -> ys | Cons(x, xs') -> rev xs' Cons(x, ys) in rev lst Nil ;; Error: The constructor Cons expects 1 argument(s), but is applied here to 0 argument(s) # let reverse lst = let rec rev xs ys = match xs with Nil -> ys | Cons(x, xs') -> rev xs' (Cons(x, ys)) in rev lst Nil ;; val reverse : 'a list -> 'a list = <fun> # reverse Cons(3, Cons(41, Nil));; Error: This function has type 'a list -> 'a list It is applied to too many arguments; maybe you forgot a `;'. # reverse(Cons(3, Cons(41, Nil)));; - : int list = Cons (41, Cons (3, Nil)) # (These error messages look appalling, but the OCaml interpreter was underlining my errors, which of course didn't paste.) Similarly, there are problems that become much easier with other paradigms of programming, such as backtracking search.
- rr808 5y ago
  Honestly I dont know the answer for this, its a trick you never need in the real world, but maybe it does test if you did compsci 101. I failed this as a Senior dev inverviewee, went back and learnt it so was preprared for the next time. It didn't make me a better programmer but now shows I've learned the basic tricks.
  - sasquatch_9 5y ago
    What is the trick in reversing a linked list? The solution is just some while loops... Anyways it is a bad question to ask because it is very easy and is frequently studied so candidates just memorise the answer.
    - rr808 5y ago
      One while loop. Maybe you need to memorize again :).
      - seba_dos1 5y ago
        There's no need to memorize anything at all; if you can code you can come up with a solution on your own within at most minutes.
      - sasquatch_9 5y ago
        I do not need to memorize it that was the point I was making, as it is so simple I can and have worked it out on the spot.
  - deleted 5y ago
    [deleted]
- hajile 5y ago
  Do you remember all the time in college where your professor explained the intricacies of cache hits, access latencies, and branch prediction when going over algorithms? As it turns out, designing a fast algorithm involves a lot more than what is covered in the textbooks. This is why something like Timsort can generally outperform quicksort even though a naive algorithms course overview may well come to the opposite conclusion. If my job is not to design these algorithms, why does it matter if I can write a naive implementation of one?
  - ThrowawayR2 5y ago
    Kind of a coincidence that you should bring that up since several jobs I've been at involved stints analyzing performance and identifying bottlenecks in existing code and it is, unfortunately, rather easy to glue together even well designed libraries in ways that result in a slow, inefficient result. Developers simply cannot get away with not knowing how their tools and libraries work under the hood.
    - Apocryphon 5y ago
      Sounds like the state of CS education should be improved to fill in those gaps of knowledge.
    - hajile 5y ago
      Choosing the correct algorithm is a different question from implementing the correct algorithm.
  - kragen 5y ago
    It matters because "algorithm" is just another word for "program". The question is whether you can think up a way to make the computer do what you want it to do at all at the level after FizzBuzz, even when it's something like reversing a linked list that can be done in two lines of code (see https://news.ycombinator.com/item?id=30616573 https://news.ycombinator.com/item?id=30616573, or seven in C), even when it doesn't need to be fast. I mean, it's true that there's a lot of code that really is at the FizzBuzz level: switch (c) { case 'h': case 'D': menu.left(); break; case 'j': case 'B': menu.down(); break; case 'k': case 'A': menu.up(); break; case 'l': case 'C': menu.right(); break; default: /* no op */ break; } def find(self, name): for thing in self.contents: if thing.is_a(name): return thing vaders.hits(bullets, (vader, bullet) => { blam(vader, 2.5) score += vader.bounty vader.die() bullet.die() }) if (vaders.where(({y}) => y > 400).count()) startGame(120) if (!vaders.count()) startLevel() And I think you should write as much of your code as possible in such a painfully obvious way. Every once in a while, though, you do need to write something that can't be written quite that simply. Often, the reason why is something in your problem domain: async def take_token(self): self.update() while not self.tokens: await asyncio.sleep(self.recharge / 10) self.update() self.tokens -= 1 // Animate explosions. poof.move() poof.each(p => {if (--p.ttl < 0) p.die()}) // Chain-reaction explosions. poof.about_every(64).each(p => { if (poof.count() < 1024) blam(p, p.w/12) }) // Limit number of explosion objects to guarantee responsivity if (poof.count() > 1024) poof.about_every(2).die() You need to be able to reason through what your code will do once you've written it, and you need to be able to come up with possible ways to write it that might work. Often the code you need for your problem domain isn't already in the standard library, so you have to write it. If it's on npm, you have to be able to read it to see whether it might work. Reversing a linked list is just about the simplest task that requires that kind of reasoning, and it has the advantage (or disadvantage) that understanding the puzzle doesn't require, or benefit from, any problem-domain knowledge. You could substitute binary search or insertion sort or something. Another example I got, which takes a few more lines of code, was "implement an integer stack ADT which can always tell you the maximum number on the stack in constant time".
mooreds 5y ago
> If someone successfully works shipping code but can't reverse a linked list, does that mean they're lying about being able to code? No, I think it means they didn't prepare. But, short of examining git commits, how can you know that someone successfully "shipped code"? References, maybe (though that is harder for folks who may have fewer references from past jobs). If it is open source, sure. But how else? > I've seen way to many jobs that test for expert level skills for a job that is just to add small enhancements. Yes, I agree! That is a bigger issue, where the job desc/interview are disjoint from the actual work. That's a red flag. It's hard, as a hiring manager, though, to keep the job desc real. I find that I sometimes throw wish list items in ("knows <tech> at an intermediate level") because the alternative ("can learn <tech>") is so hard to test for. But as a candidate I find it extremely aggravating. I don't know how to square that circle. If you figure it out, please let me know. My favorite kind of interview (on both sides of the table) is where I can do the work that is typical, using the resources that would be available on the job.
et-al 5y ago
Then problem is in the questions being asking for the technical interviews. I agree Leetcode questions are generally not a good signal because they're often removed from everyday problems one may encounter. Though they may be fun to do. If I could get a job just solving Leetcode problems, I might chose it over refactoring messy codebases or joining disparate APIs.
amusedcyclist 5y ago
Reversing a linked list is pretty straightforward. This is going to be unpopular, but i wouldn't hire someone who can't write a program to do that.
- sasquatch_9 5y ago
  Agreed, it is concerning 'senior' engineers are saying they can't do it.
  - amusedcyclist 5y ago
    This is why I'm convinced titles means nothing unless you're talking specific levels at a well established company. Often super duper Staff+ engineers or CTOs at no name startups often have 0 idea what they're doing
seba_dos1 5y ago
> If someone successfully works shipping code but can't reverse a linked list, does that mean they're lying about being able to code? On a whiteboard? Probably not. In front of a computer, with a compiler and manpages handy, being able to test and debug it right away? Absolutely, yes.

by rr808 5y ago

ThrowawayR2 5y ago

> "If someone successfully works shipping code but can't reverse a linked list, does that mean they're lying about being able to code?" Obviously yes? That's a basic assignment for a data structure class given to freshmen and sophomores. One would expect that a "senior" developer (degreed or self-taught) would be better than a college sophomore. At the FAANG level, it would be a phone screen question and a softball one at that.

mooreds 5y ago
I've held several senior developer positions and I'd have to study up on how to reverse a linked list. (Other than the obvious answer: "use a library/built-in function to do it", which would probably would not be a satisfactory answer.) I think the problem is that there are over a dozen different kinds of "seniority" but we collapse them all into one term. I got so frustrated I wrote a blog post about it: https://www.mooreds.com/wordpress/archives/2812 https://www.mooreds.com/wordpress/archives/2812
- kragen 5y ago
  It might depend on what the measure of "senior developer" is. There are junior-developer positions where nobody could perform adequately without being comfortable manipulate linked data structures (Linux kernel development, maybe, or working on a garbage collector or JIT compiler or the Postgres query optimizer) but senior developers on those teams probably don't know a tenth of what you know about SQL. Also there are ancillary skills that make the problem much less difficult, so if you can't solve it, you don't have them. Joel Spolsky famously said that nobody can reverse a linked list without drawing diagrams on paper, and that's probably true if you're doing it imperatively in C. But it's in the category of "problems that become much simpler with functional styles of programming." The following took me 5 minutes, most of which was struggling with the syntax of OCaml that I'd forgotten: $ ocaml OCaml version 4.08.1 # type 'a list = Cons of ('a * 'a list) | Nil;; type 'a list = Cons of ('a * 'a list) | Nil # Cons(3, Cons(41, Nil));; - : int list = Cons (3, Cons (41, Nil)) # let reverse lst = let rec rev xs ys = match xs with Nil -> ys | Cons(x, xs') -> rev xs' (Cons(x, ys)) in rev lst Nil ;; val reverse : 'a list -> 'a list = <fun> # reverse(Cons(3, Cons(41, Nil)));; - : int list = Cons (41, Cons (3, Nil)) The full session with all my dumb errors: $ ocaml OCaml version 4.08.1 # type 'a list = Cons of ('a * 'a list) | Nil;; type 'a list = Cons of ('a * 'a list) | Nil # Cons 3 (Cons 41 Nil) ;; Error: Syntax error # Cons(3, Cons(41, Nil));; - : int list = Cons (3, Cons (41, Nil)) # let reverse lst = let rec rev xs ys = match xs with Nil -> ys | Cons(x, xs') -> rev xs' Cons(x, ys) ;; Error: Syntax error # let reverse lst = let rec rev xs ys = match xs with Nil -> ys | Cons(x, xs') -> rev xs' Cons(x, ys) in rev lst Nil ;; Error: The constructor Cons expects 1 argument(s), but is applied here to 0 argument(s) # let reverse lst = let rec rev xs ys = match xs with Nil -> ys | Cons(x, xs') -> rev xs' (Cons(x, ys)) in rev lst Nil ;; val reverse : 'a list -> 'a list = <fun> # reverse Cons(3, Cons(41, Nil));; Error: This function has type 'a list -> 'a list It is applied to too many arguments; maybe you forgot a `;'. # reverse(Cons(3, Cons(41, Nil)));; - : int list = Cons (41, Cons (3, Nil)) # (These error messages look appalling, but the OCaml interpreter was underlining my errors, which of course didn't paste.) Similarly, there are problems that become much easier with other paradigms of programming, such as backtracking search.
rr808 5y ago
Honestly I dont know the answer for this, its a trick you never need in the real world, but maybe it does test if you did compsci 101. I failed this as a Senior dev inverviewee, went back and learnt it so was preprared for the next time. It didn't make me a better programmer but now shows I've learned the basic tricks.
- sasquatch_9 5y ago
  What is the trick in reversing a linked list? The solution is just some while loops... Anyways it is a bad question to ask because it is very easy and is frequently studied so candidates just memorise the answer.
  - rr808 5y ago
    One while loop. Maybe you need to memorize again :).
    - seba_dos1 5y ago
      There's no need to memorize anything at all; if you can code you can come up with a solution on your own within at most minutes.
    - sasquatch_9 5y ago
      I do not need to memorize it that was the point I was making, as it is so simple I can and have worked it out on the spot.
- deleted 5y ago
  [deleted]
hajile 5y ago
Do you remember all the time in college where your professor explained the intricacies of cache hits, access latencies, and branch prediction when going over algorithms? As it turns out, designing a fast algorithm involves a lot more than what is covered in the textbooks. This is why something like Timsort can generally outperform quicksort even though a naive algorithms course overview may well come to the opposite conclusion. If my job is not to design these algorithms, why does it matter if I can write a naive implementation of one?
- ThrowawayR2 5y ago
  Kind of a coincidence that you should bring that up since several jobs I've been at involved stints analyzing performance and identifying bottlenecks in existing code and it is, unfortunately, rather easy to glue together even well designed libraries in ways that result in a slow, inefficient result. Developers simply cannot get away with not knowing how their tools and libraries work under the hood.
  - Apocryphon 5y ago
    Sounds like the state of CS education should be improved to fill in those gaps of knowledge.
  - hajile 5y ago
    Choosing the correct algorithm is a different question from implementing the correct algorithm.
- kragen 5y ago
  It matters because "algorithm" is just another word for "program". The question is whether you can think up a way to make the computer do what you want it to do at all at the level after FizzBuzz, even when it's something like reversing a linked list that can be done in two lines of code (see https://news.ycombinator.com/item?id=30616573 https://news.ycombinator.com/item?id=30616573, or seven in C), even when it doesn't need to be fast. I mean, it's true that there's a lot of code that really is at the FizzBuzz level: switch (c) { case 'h': case 'D': menu.left(); break; case 'j': case 'B': menu.down(); break; case 'k': case 'A': menu.up(); break; case 'l': case 'C': menu.right(); break; default: /* no op */ break; } def find(self, name): for thing in self.contents: if thing.is_a(name): return thing vaders.hits(bullets, (vader, bullet) => { blam(vader, 2.5) score += vader.bounty vader.die() bullet.die() }) if (vaders.where(({y}) => y > 400).count()) startGame(120) if (!vaders.count()) startLevel() And I think you should write as much of your code as possible in such a painfully obvious way. Every once in a while, though, you do need to write something that can't be written quite that simply. Often, the reason why is something in your problem domain: async def take_token(self): self.update() while not self.tokens: await asyncio.sleep(self.recharge / 10) self.update() self.tokens -= 1 // Animate explosions. poof.move() poof.each(p => {if (--p.ttl < 0) p.die()}) // Chain-reaction explosions. poof.about_every(64).each(p => { if (poof.count() < 1024) blam(p, p.w/12) }) // Limit number of explosion objects to guarantee responsivity if (poof.count() > 1024) poof.about_every(2).die() You need to be able to reason through what your code will do once you've written it, and you need to be able to come up with possible ways to write it that might work. Often the code you need for your problem domain isn't already in the standard library, so you have to write it. If it's on npm, you have to be able to read it to see whether it might work. Reversing a linked list is just about the simplest task that requires that kind of reasoning, and it has the advantage (or disadvantage) that understanding the puzzle doesn't require, or benefit from, any problem-domain knowledge. You could substitute binary search or insertion sort or something. Another example I got, which takes a few more lines of code, was "implement an integer stack ADT which can always tell you the maximum number on the stack in constant time".

mooreds 5y ago

> If someone successfully works shipping code but can't reverse a linked list, does that mean they're lying about being able to code? No, I think it means they didn't prepare. But, short of examining git commits, how can you know that someone successfully "shipped code"? References, maybe (though that is harder for folks who may have fewer references from past jobs). If it is open source, sure. But how else? > I've seen way to many jobs that test for expert level skills for a job that is just to add small enhancements. Yes, I agree! That is a bigger issue, where the job desc/interview are disjoint from the actual work. That's a red flag. It's hard, as a hiring manager, though, to keep the job desc real. I find that I sometimes throw wish list items in ("knows <tech> at an intermediate level") because the alternative ("can learn <tech>") is so hard to test for. But as a candidate I find it extremely aggravating. I don't know how to square that circle. If you figure it out, please let me know. My favorite kind of interview (on both sides of the table) is where I can do the work that is typical, using the resources that would be available on the job.

et-al 5y ago

Then problem is in the questions being asking for the technical interviews. I agree Leetcode questions are generally not a good signal because they're often removed from everyday problems one may encounter. Though they may be fun to do. If I could get a job just solving Leetcode problems, I might chose it over refactoring messy codebases or joining disparate APIs.

amusedcyclist 5y ago

Reversing a linked list is pretty straightforward. This is going to be unpopular, but i wouldn't hire someone who can't write a program to do that.

sasquatch_9 5y ago
Agreed, it is concerning 'senior' engineers are saying they can't do it.
- amusedcyclist 5y ago
  This is why I'm convinced titles means nothing unless you're talking specific levels at a well established company. Often super duper Staff+ engineers or CTOs at no name startups often have 0 idea what they're doing

seba_dos1 5y ago

> If someone successfully works shipping code but can't reverse a linked list, does that mean they're lying about being able to code? On a whiteboard? Probably not. In front of a computer, with a compiler and manpages handy, being able to test and debug it right away? Absolutely, yes.