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Comment by ant6n | Hacker News Reader

It looks like there are a bunch of programmers who think that having taken the first year uni course on data structures is more important than having experience actually building product and having it used by millions.

It's kind of silly. Most programmers out of school have a lot to learn about building product and actually getting a big project done - which they are supposed to learn on the job. At a place like Google. Somebody who knows this part already could probably spend some time on the job learning about data structures.

It's like these conventionally-taught programmers think they get to look down on somebody who actually built something cuz he's self-taught. (As a conventionally-taught programmer who is very comfortable with data structures I find that attitude aloof at best)

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I have a traditional Computer Science background and I'm still intimidated to even apply to Google. I got out of bigCo Software Engineering in part because I wasn't interested in putting myself through the wringer of whiteboarding memorized solutions.

I'm also the guy that found low hanging fruit in a huge codebase to replace things like frequent linear array lookups with hash table lookups for 10x+ speed improvements in the build process. This is IMO precisely the type of capability that "Oh, that's O(n^2), surely we can do better. Is there any way to do this in O(1)?" is designed to tease out in the interview process. I did it! In a build process effecting 1000+ engineers, used to build for millions of shipped units! But talking about this in an interview makes eyes gloss over as we prepare to move on to sort algorithm trivia, how would I design search, or doubly linked list implementations.

But you know, hash tables have O(n) access...

And this is where interviewing gets hard. Are we really going to not hire someone because hash table is O(n) in the worst case but O(1) on average. It seems like half the time there isnt a match, the interviewer is just as wrong as the candidate, and they are looking for someone who knows the same info as them, even if its half baked.

Some implementations have O(n) access in the worst case.

Often people are interested in something like the 99.9999%ile case. And, of course, you can design hash tables with better worst case behaviour.

It's almost trivial to get a hash table with O(log n) worst case access: when you have a collision, just resolve it with a tree instead of a linked list.

With some more fancy math, you can also get O(1) amortized worst case behaviour with arbitrarily high probability that doesn't depend on your input data.

See https://sockpuppet.org/blog/2015/03/06/the-hiring-post/

> It looks like there are a bunch of programmers who think that having taken the first year uni course on data structures is more important than having experience actually building product and having it used by millions.

To be honest, drilling down on all the stuff they teach you in first year helps you more in getting a job at Google than having lots of practical experience.

I'm inclined to believe that this is a problem with Google. But I am not sure you should trust my opinion: I am sure Google spent much more time and money and figuring out the right approach here than I ever laid my hands on in my whole life.

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