Hacker News Reader

Comment by codingdave | Hacker News Reader

>"Not off the top of my head, no."

They were probably looking for the answer of, "Lets talk through it and figure out a better answer". Coders are often under a mistaken impression that interviewers care about your answer. They don't. They care about how you approach it, how you think through it, what you do when challenged, etc.

So from their perspective, they asked you to try harder on a problem, and you just said, "No." And they dropped you for it.

FWIW, I had similar questions in some interviews where we hashed through similar problems, and together collaborated down to a "No" answer... but we spent 15 minutes exploring the problem and seeing how well a couple coders can work through it before saying no. And I got the offer despite an otherwise rusty performance.

View on HN

> Coders are often under a mistaken impression that interviewers care about your answer. They don't. They care about how you approach it, how you think through it, what you do when challenged, etc.

This isn't always true. Some interviews are really about solving the problems as fast as possible. And lots of interviewers are looking for exactly the answer they have on hand, and will think you're doing it wrong if you come up with a different, but equally valid (or better!) solution.

In which case, I don't think that's a place I'd like to work. Most often the solution an engineer comes up with is _not_ ideal and will be improved either because they come up with a better one later before they commit it or because they go through code review and someone else sees a better way. If you don't leave room for people to improve their solutions you'll just end up with the first, crappy one that comes to mind.

> They care about how you approach it, how you think through it, what you do when challenged, etc.

I was asked to sketch the proof for the irrationality of sqrt(2) in a quant programming interview. I kind of froze, and explained that though I had learned it, I could not recall.

He prompted me with "Well, what does it mean to be irrational?", and with that little hint I did the rest. Though ultimately I did not end up working there, it was very satisfying to have answered it.

A friend of mine didn't understand how he could have done better than me in a "write a quick sort" interview (we were still students) when I knew the algo and he never heard of it (and obviously struggled more).

Well, in one case (me), all the information the interviewer had was "this guy happens to know how to implement a quick sort by heart. K.".

In the other case (my friend), he got "this guy is able to understand and implement an algo he never saw before in a reasonable time", which is much more impressive

Errr in the set of numbers that complete the rationals wrt to standard metric? I guess you have to show it’s not rational so you probably did a proof of upper/lower converging bounds always having nonzero difference for 1/n increments or something? I would definitely not get this in a pressure interview situation.

From what I remember, it's simpler than that:

Assume sqrt(2) is rational and has the reduced form (x/y). Thus we are assuming that x and y are integers and that gcd(x,y) is 1. You square it and get x^2/y^2 which are somehow simultaneously coprime integers and also reducible to 2/1...

I think here they just meant, show that no rational number is the square root of 2. Not rational = not expressible as a ratio. You assume that sqrt(2) = p/q for some integers p and q, then derive a contradiction.

Here's the proof from Baby Rudin:

> We now show that the equation (1) p^2=2 is not satisfied by any rational p. If there were such a p, we could write p=m/n where m and n are integers that are not both even. Let us assume this is done. Then (1) implies (2) m^2=2n^2. This shows m^2 is even. Hence m is even (if m were odd, m^2 would be odd), and so m^2 is divisible by 4. It follows that the right side of (2) is divisible by 4, so that n^2 is even, which implies that n is even. > The assumption that (1) holds leads to the conclusion that both m and n are even, contrary to our choice of m and n. Hence (1) is impossible for rational p.

> Coders are often under a mistaken impression that interviewers care about your answer. They don't.

Huge asterisk that as long as you arrive to the correct solution with minimal help. I've had plenty of algo/ds interviews and it seems like needing help to see the trick in the question pretty much means you're out.

> Coders are often under a mistaken impression that interviewers care about your answer. They don't. They care about how you approach it, how you think through it, what you do when challenged, etc.

In many of the places that do claim this, even if you solve the problem "correctly" you still get more brownie points than someone who got a less efficient answer or didn't get an answer. Meaning that they /do/ actually care. I do get that some places are smarter with regards to this than others but it's depressingly common in my experience. "You didn't get the O(n) solution that has weird edge cases and was published as a paper in the 70s? Too bad, because some other person did, because they remember the solution from some programming interview book!"

Then I'd argue they need to make that more clear. The typical interview setting does not suggest it's an "exploratory" environment, it usually feels more like taking an exam.

At my last company, we would sit a candidate down at a pairing station. We'd offer them about 5 problems to choose from, and together we'd pair program on the problem for 2 hours. Using the internet, the IDE, anything they want was totally fair game. No system is perfect, but this was by far the best one I've ever experienced.

Reply on news.ycombinator.com