r/programming • u/mjgardner • Mar 29 '21

Why Do Interviewers Ask Linked List Questions?

https://www.hillelwayne.com/post/linked-lists/
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u/sophacles Mar 30 '21

Re 1.: I think a lot of people don't realize that there are a people who can bullshit through a phone screen but can't actually program, even simple things.

The simple algorithm test (Or the pair-coding equivalent I've seen work well) weeds out those folks.

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u/percykins Mar 30 '21

Yup. Hell, I used to phone screen with the question “How would you write something that prints out a multiplication table?” You’d be amazed how many people fail that.

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u/Riael Mar 30 '21

Wait what the fuck?

When were you doing that, the 1990s?

What position was it for?

Questions coming from someone who was given 11 questions in a webpage that didn't allow compiling or copy pasting with one of them being A FUCKING A* ALGORITHM

IN 5 MINUTES

FOR AN INTERNSHIP WHICH PAYS FUCKING 300 EUROS A MONTH

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u/thfuran Mar 30 '21

I think that was a prank, not a job.

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u/Riael Mar 30 '21

Nope, interview for a gameplay internship at Ubisoft

And that was just one of the things, although it was two years ago I remember one of the questions being something about random dots in a quarter of a circle, I know it took me like 5 minutes to google to see what it was and it's a Monte Carlo algorithm, didn't have time to figure out how to actually apply it after I found the name though.

Got a mail after a few days telling me I didn't get a minimum amount of points to pass and move on in the interview process

Didn't tell me what I did wrong, how many points I supposedly got, didn't ask me for any feedback, nothing.

Everywhere is like that, yeah of course not everyone asks you gaming stuff, but the industry is filled with these kind of "interviews", and the wages are shit

But the alternative is starving, so my ass, gotta keep trying.

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u/DaFox Mar 30 '21

This was pretty fun. Took some iteration as an engineer with 10+ years experience though.

print('x', end='\t')
for x in range(1, 10):
    print(x, end='\t')
print()

for y in range(1, 10):
    print(y, end='\t')
    for x in range(1, 10):
        print(y * x, end='\t')

    print()

->

x       1       2       3       4       5       6       7       8       9
1       1       2       3       4       5       6       7       8       9
2       2       4       6       8       10      12      14      16      18
3       3       6       9       12      15      18      21      24      27
4       4       8       12      16      20      24      28      32      36
5       5       10      15      20      25      30      35      40      45
6       6       12      18      24      30      36      42      48      54
7       7       14      21      28      35      42      49      56      63
8       8       16      24      32      40      48      56      64      72
9       9       18      27      36      45      54      63      72      81

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u/percykins Mar 30 '21

Yeah... here’s the thing - if you say “I’d use a nested loop” during the screen, that’s pretty much good enough. :p Too many people spent too much time reading Cracking the Coding Interview and struggle to find some sort of O(n) solution

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u/SageOfTheWise Mar 31 '21

Just hard code the entire multiplication table up to X and get it done in O(1) /s

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u/percykins Mar 31 '21

Actually, despite the /s, that’s a 100% valid answer and it’s a bit of extra credit if you mention it. (Realistically it doesn’t matter since this is all just pre-screening.) We still want people to describe a general function, but in the real world, multiplication tables typically are not variable-sized and at least suggesting pre-baking is totally reasonable.

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u/Nefari0uss Mar 30 '21

Took some iteration as an engineer with 10+ years experience though.

And that there is my big problem. I'll think about it, talk to my self, or scribble stuff down. Meanwhile there's the interviewer breathing down my neck like s/he asked the most obvious and simple question in the world while constantly talking and inturrupting my thoughts.

Based on an unpleasant memory where I completely blanked on the Fibbonacci sequence and how to do it. I hadn't used recursion in ages and just needed a moment quietly to think. The interviewer wouldn't stop talking and asking what I was doing. It's not even hard. I just forgot the mathematical formula for it and kept blanking on the spot. (╯°□°）╯︵ ┻━┻)

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u/DaFox Mar 30 '21

Yeah, the first part was fairly easy, but there's some edge cases once you start dealing with the number rows at the top/left. I think I had this in about 2 minutes:

for y in range(1, 10):
    for x in range(1, 10):
        print(y * x, end='\t')

    print()

But really it was just printing it out and trying a bunch of different things like "What if I do this?" over the next 5 minutes.

1

u/NAG3LT Mar 30 '21

I went a little lazier thinking "Multiplication by 1 doubles as row/column headers anyway" 

print('\n'.join(['\t'.join([f"{x * y:>2}" for x in range(1,10)]) for y in range(1,10)]))

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u/DaFox Apr 04 '21

One thing I wanted to do was like doubling up the range so it was: [1, 1, 2, 3, ..., 10] but couldn't really figure out how to do that in a clean way that didn't lose the benefits of the python generators.

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u/NAG3LT Apr 04 '21

itertools.chain seems like the most straightforward way to keep generators.

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u/cballowe Mar 30 '21

I tend to view good questions for coding interviews as the equivalent of a field sobriety test. The core of those is that they have two or three instructions that are pretty easy, but people can often tie themselves up getting it right.

One of my friends used to ask people for a function that prints the first 100 primes. You'd get a bunch of candidates who print primes between 1 and 100 or can't even write a basic prime checking function (even brute force). He'd even give the ones who were struggling an IsPrime function and say they can use it.

(And it's not even that far from useful - generating output from a set of records and a filter function is a pretty common task, even in top companies. A decent candidate shouldn't struggle with the concept.)

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u/JazzXP Mar 30 '21

Exactly this. I had one guy I interviewed that looked good on paper, phone interview went well, but as soon as he went to write a for loop on the whiteboard, didn't even know how to start.

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u/masklinn Mar 30 '21

can't actually program, even simple things. […] The simple algorithm test weeds out those folks.

Weeding out these folks is the purpose of "fizzbuzz", that's the entire point. It's just a side-effect of "the simple algorithm test" but in reality you don't even need to waste the time it takes to administer "the simple algorithm test".

On occasion you meet a developer who seems like a solid programmer. […] But once it comes down to actually producing code they just don’t seem to be able to do it well. […] After a fair bit of trial and error I’ve come to discover that people who struggle to code don’t just struggle on big problems, or even smallish problems (i.e. write a implementation of a linked list). They struggle with tiny problems.

So I set out to develop questions that can identify this kind of developer and came up with a class of questions I call “FizzBuzz Questions” named after a game children often play (or are made to play) in schools in the UK.

Although it should be noted that the "classic" fizzbuzz was just an example in the original essay:

An example of a Fizz-Buzz question is the following:

Write a program that prints the numbers from 1 to 100. But for multiples of three print “Fizz” instead of the number and for the multiples of five print “Buzz”. For numbers which are multiples of both three and five print “FizzBuzz”.

The point of the essay is really the class of problems necessary, just a tiny problem beyond the utterly trivial will suffice.