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Comment by jiggawatts | Hacker News Reader

There was a hilarious rant about a FAANG hiring question that was something like: "Write an algorithm for detecting if a linked list has any loops in it, in linear time, using a constant amount of memory."

Apparently the correct answer is to use "Robert W. Floyd's tortoise and hare algorithm", which is trivial to explain and code.

The catch?

It took a decade of computer science research between the original statement of the problem and Floyd discovering the solution.

So... no worries, you have an hour, a marker, and a whiteboard. Your time starts: now.

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I'm just imagining an engineer coming up with a novel solution to this problem in under the hour deadline and then not getting hired because it's not the "Robert W. Floyd's tortoise and hare" algorithm.

"So we specifically asked for linear time."

"Uh, yeah, I did it in log(n). That's better."

"It doesn't match what's on this paper they gave me. Thanks for your time. We'll be in touch."

it took a few million years until Newton figured out basic mechanics. but i don't think it's unreasonable to ask a junior engineer some basic kinematics questions!

Subtly different, IMO.

You’re expecting the mechanical engineer to recall something they learned about kinematics, not derive it on the spot. It’s a test of knowledge, rather than cleverness. The equations of motion are also more central to physics and engineering.

A decent programmer should know that linked lists exist, their general properties, pros and cons, etc. However, cycle detection is not a particularly common operation, so not knowing Floyd’s algorithm tells you very little—-and their failure to do years of research in 45 minutes even less.

Yeah, I think a closer analogue would be asking something like "derive the conserved quantities of the gravitational two-body problem" and then dinging candidates for forgetting about the Laplace-Runge-Lenz vector

A software engineer? Sounds totally unreasonable. A mechanical engineer, sure, it's going to be required material on their education.

The tortoise and hare algorithm is not the foundational skill required to make software work the way an understanding of motion is for building structures. That's why it's often omitted from educational material yet these people are able to produce usable software after even something like a bootcamp (which I guarantee basically no bootcamps ever touched this algorithm).

I'm not sure I approve of asking even more well known algorithms like Djikstra's algorithm or A* in a job interview, unless the role was something that specifically required that area of knowledge like building pathfinders for video games or robots or something.

It would bias toward people who are comfortable doing basic calculus on a whiteboard.

Also, it took around 13.8 billion years for Newton to do what he did.

ya its dumb, but also CTCI question 4 or something or linkedlist chapter

This is exactly the point!

If they actually aren't looking for people who just cram CTCI or leetcode, coming to this answer from first principles is demonstrably far more difficult than you'd expect achieved in an interview.

Which becomes forgotten knowledge in about 6 - 12 months time after you've last needed to apply it, depending on how often you'd have to use that information.

These sort of questions have an incredible recency bias, and have zero relevance to engineering competence.

I have a theory that these q's legally favor recent grads without having any explicit requirement to do so. Helps them filter for young, freshly-trained students who they can mould into whatever they like inside of the FAANG-bubble.

> These sort of questions have an incredible recency bias

Of course; how else do you do back-door age discrimination?

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