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Inverting Binary Trees Considered Harmful

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Re: Inverting Binary Trees Considered Harmful

#41

Post by mrcsparker »

BobTheCoder wrote: post #27

A lot of these posts don't actually address the problem of hiring and filtering people. If you think whiteboard tests or logic puzzles are not effective, why do you think this and what is a better alternative? I personally think they are ok, but should more be a means to test if the candidate can reason intelligently and it shouldn't matter much if the end answer they get is correct or not.

I always try to find out if the candidate could - with enough information - solve the puzzle.

Can you, given time, figure out a good solution to the problem I am asking? How would you go about solving the problem? What is your methodology?

I agree with you. These sorts of problems are really to understand how someone reacts to a new idea that he or she does not understand. A lot of times people tell me that they don't know they answer to a problem, which is fine. Knowing that there are things that we don't know if a sign of maturity, and the curiosity to figure out how to solve a problem is what we should be looking for.

Re: Inverting Binary Trees Considered Harmful

#42

Post by rayiner »

I don't think inverting binary trees is the problem per se. I mean, algorithms are the bread and butter of programming. You should be able to implement simple ones like that even if you'd never actually do that in practice. The real problem in my opinion is the whiteboard and time pressure.

Re: Inverting Binary Trees Considered Harmful

#43

Post by orangecat »

I'll be the contrarian and claim that inverting a binary tree is a perfectly reasonable interview question. (Although not anymore now that it's famous). It combines basic background knowledge (what is a binary tree and how is it structured?), ability to reason logically (binary tree algorithms are often recursive, "inverting" a tree with no children is a no-op, otherwise you want to swap the children, and the children's children, and...), and enough familiarity in one language to write simple constructs without an IDE or stackoverflow holding your hand. None of this requires you to be Jeff Dean.

I will agree that the guy who kicked all this off has a legitimate complaint if the recruiter failed to adequately explain the interview process, and I'm sure there are lots of bad interviewers that focus on meaningless details or obscure trivia. But I don't agree that the concept of having candidates write code is fundamentally awful.

Re: Inverting Binary Trees Considered Harmful

#44

Post by gnuvince »

derekp7 wrote: post #20
smaili wrote: post #8

While I'm completely, 100%, against these kinds of questions, how else can a company that receives thousands of resumes a day filter out the good from bad?

How about sitting the candidate down in front of an actual computer, or ask the candidate to bring in their own laptop? Then if you want to see how they do, pick out some open source projects that need a feature or two added, or a bug fixed, and have the candidate walk through some solution? This way, you are getting to see what their style is, and the random open source projects gets a potential improvement. And you…

So instead of giving them an algorithm problem that they might have seen in the past (or seen something similar) you give them a random open source project -- along with all the idiosycracies it certainly contains -- that they are 100% unfamiliar with and ask them within a few minutes to make sense of the entire codebase and produce a meaningful contribution? Sorry, but that sounds even more cruel and unusual than asking a very obscure algorithm question.

Re: Inverting Binary Trees Considered Harmful

#45

Post by sanxiyn »

BobTheCoder wrote: post #27

A lot of these posts don't actually address the problem of hiring and filtering people. If you think whiteboard tests or logic puzzles are not effective, why do you think this and what is a better alternative? I personally think they are ok, but should more be a means to test if the candidate can reason intelligently and it shouldn't matter much if the end answer they get is correct or not.

Work sample tests, of course. Basically everybody who read the literature knows what is the better alternative.

Re: Inverting Binary Trees Considered Harmful

#46

Post by [deleted] »

rdtsc wrote: post #11

Yeah I remember the Google interview a few years back. I did it mostly for fun, and because their recruiters kept contacting me. So there we were, building a tree out of a forest of existing smaller trees or such. That was after they couldn't find my resume, and used a 5 year old one they found some place. They seemed annoyed and tired. By that time I felt nothing short of me proving P!=NP would have help changed the…

[deleted]

Re: Inverting Binary Trees Considered Harmful

#47

Post by ashwinaj »

scotth wrote: post #37

Fact is, it just isn't true. As a Googler, I am surrounded by enormously talented engineers, the likes of which I rarely encountered on the outside. They love what they do, and it shows. I have no doubt that there are false negatives/positives, but I am convinced that Google is doing something right.

Have you encountered anyone outside? Sure there are talented engineers there but so are engineers in startups and other companies. I'm afraid that's a very myopic statement.

Re: Inverting Binary Trees Considered Harmful

#48

Post by Osiris »

The last interview I did was for a node.js position. I was told to bring my laptop. When I got there, the put me in an office and handed me a packet with instructions on checking out a nearly empty git repo. Then they said "Write an API that meets as many of the following requirements as possible and push the code. We'll be back in 3 hours."

After 3 hours, I was taken to a conference room where I demonstrated the API. I also talked about a bug I had that had hung me up, but I fixed it right there in the conference room.

Got the offer. It was a great experience. I enjoyed the challenge, but it felt useful and related to the work rather than just esoteric problem that would not likely ever be required by the job, and if it was I'd have time to research it and figure it out.

Re: Inverting Binary Trees Considered Harmful

#49

Post by mrcsparker »

wyager wrote: post #3

>You are then ushered into a room with the programmer's worst nightmare - a blank whiteboard. Am I the only one who enjoys programming interviews? Even if you screw it up, it's still fun to try your hand at whatever problem they give you. They also don't expect you to do it perfectly; you're allowed to have sub-superhuman performance.

I love them too. Lots of brilliant people have trouble solving problems while a group of strangers are staring at them.

Part of the interview process is trying to find out what type of person you are dealing with.

Re: Inverting Binary Trees Considered Harmful

#50

Post by melling »

rdtsc wrote: post #11

Yeah I remember the Google interview a few years back. I did it mostly for fun, and because their recruiters kept contacting me. So there we were, building a tree out of a forest of existing smaller trees or such. That was after they couldn't find my resume, and used a 5 year old one they found some place. They seemed annoyed and tired. By that time I felt nothing short of me proving P!=NP would have help changed the…

I was told by someone many years ago to always take a copy of my resume with me to an interview. That advice has paid off a couple of times. These days I also keep an email draft ready to send.
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