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Google's “Director of Engineering” Hiring Test

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1764 points fatihky | 5 comments | 13 Oct 16 15:15 UTC | HN request time: 0.001s | source
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lordnacho ◴[13 Oct 16 15:43 UTC] No.12701486[source]▶
I'm amazed he knew things in such detail. I mean who would know just how long a MAC address is? Or what the actual SYN/ACK etc tcp flags are? You just need to know what they're used for, and if you need the specifics, you'll find out with a single search. He seemed to know that as well though. Kernighan for bit twiddling algos, that kind of thing.

It's a bit strange to have someone non-technical interviewing a techie. You end up with stupid discussions like the one about Quicksort. If you point out qs is one of several things with the same big-O, you'll probably also get it "wrong". But the real problem is that a guy who is just reading off a sheet can't give any form of nuanced feedback. Was the guy blagging the sort algo question? Did he know if in detail? Does he know what the current state of research on that area is? There's no way to know that if your guy is just a recruiter, but I'm sure even a relatively junior coder would be able to tell if someone was just doing technical word salad.

I wonder what would happen if ordinary people recruited for medical doctor jobs? Would you be comfortable rejecting a guy who'd been in medical school for 10 years based on his not knowing what the "funny bone" is? Wouldn't you tell your boss that you felt a bit out of that league? It's amazing you can get someone to do this without them going red in the face.

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tptacek ◴[13 Oct 16 15:55 UTC] No.12701606[source]▶
I knew all these answers too, because I was a developer in the 1990s.

There is absolutely no purpose to knowing off the top of your head how long an ethernet address is, or even what system call will retrieve an inode (his bickering over stat() "filling in" rather than "returning" was bogus, for what it's worth). The top Google search result for each of these questions has the answer. Knowing these things isn't part of being a practicing programmer; knowing how to find out is.

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mox1 ◴[13 Oct 16 16:05 UTC] No.12701685[source]▶
The question was what function "returns" an inode.

Those functions return a error code, you pass in a stat structure and the function populates that structure.

He was saying (correctly), that they don't return (in the classic C sense) the inode. They return an error code.

To me that is a big difference...

int lstat(const char path, struct stat buf);

vs stat* lstat(const char *path);

2 completely different functions.

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1. tptacek ◴[13 Oct 16 16:35 UTC] No.12701989[source]▶
In C, what stat does is how you return multiple values from a function.

lstat has the same signature as stat: it passes the stat structure back through an output pointer.

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2. philjr ◴[13 Oct 16 16:38 UTC] No.12702014[source]▶
But not if you're a literal lunatic who thinks that because you literally used the word return with an error code that's what it returns. And. Only. That.
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3. gknoy ◴[13 Oct 16 18:29 UTC] No.12702932[source]▶
To be fair, the rest of the questions were demonstrably pedantic, and I would completely expect a question like this to be on the bill of fare:

   Q: What does lstat return?
   A: A struct
   >> Wrong, it returns an error code
That type of technical specificity about what well-known functions return is absolutely something I've heard people use as an interview question. Knowing it returns an error code (rather than the value you want) seems like a good indicator of "has actually coded in C" (whereas many other languages return the value you want and raise an exception if it had an error).
4. vram22 ◴[13 Oct 16 20:09 UTC] No.12703640[source]▶
>In C, what stat does is how you return multiple values from a function.

IIRC, you can return structs from functions in C. You have to access the values in the returned struct with dot notation, of course, like point.x .

Pre-ANSI C may not have had this, but later, it did. Remember reading it in the 2nd (ANSI) edition of the Kernighan & Ritchie C book, and also used it myself in some programs.

https://www.google.co.in/?q=can+you+return+a+structure+in+c

Edit:

Might want to consider the cost of copying, depending on the perf requirements, size of the struct, whether the function call is in a tight loop, etc.

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5. philjr ◴[14 Oct 16 10:50 UTC] No.12707239[source]▶
returning multiple values was the key part of the sentence