Ask HN: What's your speciality, and what's your "FizzBuzz" equivalent?

https://news.ycombinator.com/item?id=6999429

by ColinWright • 13 years ago

260 330 13 years ago

news.ycombinator.com

I was recently chatting with friends and the question came up: When hiring a programmer, FizzBuzz is sometimes (and controversially) used as an initial filter. What's an equivalent filter for mathematicians?

I know that HN is filled with people who have specializations outside of programming, so I ask:

    What is your specialization, and
    what is your "FizzBuzz" equivalent?

Added in edit: Fascinating answers - thank you. I'd love to respond to many of them but that would probably trip the HN flame-war detector, penalise the item, and I'd get no more replies! If you want a reply, email me, or make sure your email is in your profile. And thanks again to all.

wengzilla• 13 years ago

I was an electrical engineer before I was a computer programmer and people liked asking questions about Ohm's law and calculating total resistance of resistors in series and parallel.

EDIT: I should clarify... They weren't asking about the theory behind Ohm's law but rather to apply it to various circuits.

ColinWright9• 13 years ago

Interesting - thanks. I was hoping for more results, but with this falling rapidly off the "newest" page, and with only one upvote, I guess we won't get (m)any more insights.

Edit: Last minute surge and we're on the front page! Amazing - thanks to those who voted - I'm waiting to see if we get any more answers ...

PaulKeeble• 13 years ago

That feels more like asking the difference between a class and object. Its not really asking someone to solve nearly the simplest problem to prove they can can code.

Would the equivalent not be making a basic circuit to do something specific and hence a specific example that has one or two potential obvious issues?

walshemj3• 13 years ago

Sorry Ohms law is not like a class or an object in any way at all.

walshemj3• 13 years ago

Engineer roles or Technician?

sequoia3• 13 years ago

can you give an example? tia!

huhtenberg• 13 years ago

  A-->   +--[1 Ω]--+--[1 Ω]--+
         |         |         |
       [1 Ω]     [1 Ω]     [1 Ω]
         |         |         |
         +--[1 Ω]--+--[1 Ω]--+
         |         |         |
       [1 Ω]     [1 Ω]     [1 Ω]
         |         |         |
         +--[1 Ω]--+--[1 Ω]--+    <-- B

Find the resistance between A and B.

ColinWright9• 13 years ago

I'm a mathematician, and sometimes I need to assess the level at which I'll pitch an explanation. Although I don't do this in a setting where it's possible to set a test, as such, I do ask this question:

    An equivalence relation is reflexive, symmetric, and
    transitive.  If E is an equivalence relation, and we
    know E(x,y) but we know !E(y,z), what do we know
    about E(x,z), and why?

It seems a great filter for people who can think and reason formally, as opposed to using intuition based on their understanding of the words.

Edited in response to lmm's perfectly reasonable question. In context I would see if they just assumed they knew what I meant, or asked for clarification. If they assumed they knew what I meant, it would be interesting to see what interpretation they used. This is like FizzBuzz - it shouldn't stop with the first draft of the code - it's an opening for discussion.

lmm• 13 years ago

"we know not" seems like an unfairly trapped way of phrasing that question; it's not entirely clear that you mean "we know !E(y,z)" rather than "we don't know anything about E(y,z)".

darkrho4• 13 years ago

Re: E(x,z) is false (or !E(x,z)). Otherwise we would have E(y,z) given that E(y,x), that's a contradiction.

tel4• 13 years ago

How often do you get people who apply but cannot pass that test? I always felt that CS gets a pretty large influx of people who are very fresh to programming (as isn't everyone!) but I would have thought a math fizz buzz would need to be harder to get signal.

aaronem23• 13 years ago

I'm not a mathematician, but it looks to me like we know E(x,z) is false. The transitive property gives us

    E(x,y) & E(y,z) => E(x,z)

but since we know !E(y,z), we can infer !E(x,z).

(I'm not a logician, either, so I hope you'll excuse what may be imprecise phrasing on my part.)

danbruc• 13 years ago

Your result is correct but your reasoning is not sound. A & B => C and !B does not imply !C.

noblethrasher• 13 years ago

x is "near" y and y is near x. y is not near z, so z is not near y, and therefore z is not near x nor is x near z.

Someone• 13 years ago

Bad example. "Near" is not an equivalence relation. Every step you make keeps you near where you were, but you can eventually get thousands of miles away.

sauerbraten• 13 years ago

When !E(y,z), then also !E(z,y) (because symmetry). Also, E(y,x).

Thus !E(x,z), because E(y,x) and E(x,z) would imply E(y,z), which is false.

jules9• 13 years ago

I would definitely reason intuitively to solve this question, rather than formally. When I see E(x,y) I paint a picture in my head putting x and y in the same equivalence class:

    =======
    | x y |
    =======

When I see !E(y,z) I put a picture in my head where z is outside of the equivalence class of y (and x):

    =======    =====
    | x y |    | z |
    =======    =====

Hence we can conclude that !E(x,z). So while this is a nice question, I don't think it achieves your goal of testing formal as opposed to intuitive reasoning.

robrenaud• 13 years ago

You know about equivalence classes and know to apply them. You can reason about partitions rather than needing to drop down the the level of logical implications (higher level abstractions for the win). If you remove the "think" part and become a little bit more assertive, your intuition becomes a proof.

You pass.

YesThatTom2• 13 years ago

I have been unable to think of one for Linux system administrators. :-(

ambiate• 13 years ago

Ask about disaster recovery, backups, penetration testing, what to do if a database/webserver breach occurs, or any form of generic networking/routing.

bob_george33• 13 years ago

Not sysadmin specifically, but when I was working as a computer technician, questions we would ask to scope out the skills of people were along the lines of:

Q: "Something you have no experience with has broken and won't do a basic function, how will you go about fixing it?" A: Research, ask someone else etc.

Q: "X is missing their password for a system we have no admin rights on. How are you going to fix this?" A: Recovery Tools. Format device and set it up again. Use JS/Developer tools to get it in plain text from the browser.

octo_t2• 13 years ago

I've found 'list 10 two-letter linux commands and their use'

They don't actually have to think of 10, but their answer can show what they've actually had to do on a *nix system. Its also lets you prod them with questions like 'how might I get disk usage' or if they mention dd, ask them how they use it, what its good for etc.

icebraining3• 13 years ago

I was surprised I could actually think of 10. Using both dc and bc seems like cheating, though ;)

hacknat5• 13 years ago

Here's a couple:

Grep a current running process.

Grep x file and copy it.

You'd be surprised how many "Sys Admins" I've interviewed who can't do basic things.

EvanAnderson• 13 years ago

I've been a contract sysadmin for a long time. In a former "life" part of my work was doing phone screens and job interviews for contract sysadmin candidates.

If a candidate's answer to a nonspecific troubleshooting scenario didn't begin with (or contain very close to the beginning of the answer) "look at the logs" I'd bump them. Anybody whose problem-solving methodology doesn't including gathering pertinent data early in the process isn't somebody I want "solving" problems for me.

darkrho4• 13 years ago

Years ago I've been asked: There is a file named "-foo", how do you delete it?

aaronem23• 13 years ago

I've seen a good one -- actually got asked it in a phone screen I did last year:

"How would you recursively delete all files with extension 'mp3' in a given directory tree?"

The (simplest) correct answer (I know) is

    find /path/to/wherever -name "*.mp3" -exec rm -fv {} \;

Maybe that's more of a pons asinorum, I suppose, but then isn't a pons asinorum precisely what a fizzbuzz question is meant to be?

icebraining3• 13 years ago

The simplest would be

    find /path/to/wherever -name "*.mp3" -delete

This works at least in GNU find and FreeBSD.

presidentender2• 13 years ago

Can't we

    cd /path/to/wherever
    rm -rf *.mp3

?

falsedan5• 13 years ago

  find path -iname "*.mp3" -print0 | xargs -0 rm -fv

dasmoth• 13 years ago

That seems like a recipe for holy-war between those who kind-of like xargs and those who think find | xargs is an abomination.

chaosphere2112• 13 years ago

Alternatively, you can just use

    find /path/to/wherever -name "*.mp3" -delete

snorkel2• 13 years ago

"You need shell access to a remote system using ssh. What file would email to the admin to grant you access using ssh?"

You'd be surprised of how many supposed Linux admins have no idea how to setup ssh logins, which says a lot about the depth of their experience.

hnriot3• 13 years ago

I'd make this a requirement of developers too, some basic unix skills goes a long way as a developer.

Ologn• 13 years ago

The best question I have is "Describe the power on of a RHEL x86 system in as much detail as possible from beginning to end, each step of what happens". It is open ended but can tell you a lot. You can get very fine grained, down to the hardware signals which take place before FFFF0000 is executed.

raverbashing3• 13 years ago

1 - How to connect to a server using SSH without a password

2 - How would you check if $DATABASE is running and how would you start it if it wasn't. Bonus points: how do you make it start automatically at next reboot

3 - Show me the processes using the most CPU

sov• 13 years ago

Is 1. really that trivial? If I recall there's some really weird convention about usernames across both platforms (assuming *nix) having to be identical, in addition to fiddling around with the RSA keys.

austenallred2• 13 years ago

I'm a marketer, and have yet to find a way to judge a marketer's competence better than:

"Here's this app, here's what it does. How would you increase downloads?"

A quick brainstorm session shows you how they approach the situation, what tricks they have in their bag, and what methods they feel confident using (or if they're just BSing).

Interestingly enough, 50% of the time people answer "SEO," which is among the worst answers you could possibly give. The best answers often involve the person playing with the app and figuring out something you could actually build into the app itself.

snorkel2• 13 years ago

There's a difference between marketing and product design. A marketer should know how to get qualified leads for lowest cost to your app, and then it's your product manager who should worry about making the best impression with new users.

atroyn2• 13 years ago

This is really a false dichotomy. Many apps can market themselves by 'baking in' sharing, and I don't mean just a 'tweet/like/pin' button on every other page.

These two functions are not separate.

ddebernardy• 13 years ago

There's a difference between marketing and product design. A marketer should know how to get qualified leads for lowest cost to your app, and then it's your product manager who should worry about making the best impression with new users.

In my own experience the marketer's primary job is to identify how and why your end-users might use your product, i.e. understand who these qualified leads are to begin with.

corin_• 13 years ago

Marketing takes all sorts - there are plenty of people who do a great job by just doing SEO, or by just buying adwords, etc.

adventureloop• 13 years ago

Would the answer of the inverse question be interesting? Taking our successful landing page, how would you reduce downloads?

austenallred2• 13 years ago

That's an interesting thought, but I can't see how it would be, simply because of the sheer number of ways that would be possible. That's kind of like saying, "Here's this working program, how could you break it?"

jstanley• 13 years ago

Remove the download link.

QuantumGood2• 13 years ago

And then you ask them what they mean by SEO, and it gets worse. SEO is one of my favorite buzzphrases, because it causes ignorant marketers to rapidly self-select. (Unless their explanation shows otherwise.)

tieTYT• 13 years ago

The best answers often involve the person playing with the app and figuring out something you could actually build into the app itself.

I'm clueless when it comes to marketing. Could you elaborate here with some examples? I think the majority of apps are in a place where nobody knows they even exist, so how could improving something in them improve downloads?

er35826• 13 years ago

I'm an electrical engineer who has pared my skill list down to 'troubleshooting.' For my equivalent of a fizzbuzz, the exercise is to present someone with a potential failure (the light in the room is off) and ask them how they'd go about investigating the problem.

I like to see all kinds of answers, but particularly more theories are better, especially when justified at least loosely. Things like "change the light bulb", "flick the switch", and "check the circuit breakers" are evidence that they have the right mind for breaking a situation out into many different causes.

edit: I absolutely loathe 'out of the box' as a meme, but I love hearing responses like "is anything else in the room turned on?" as it shows a simpler, more direct way of assessment.

Piskvorrr• 13 years ago

I have misread the last quote as "is anyone else in the room turned on" and wondered whether that's not a bit far out of the box ;)

aaronem23• 13 years ago

That's not a question I've ever had cause to ask on either side of an interview, to say the least.

solox33• 13 years ago

Working for a web company. Our favourite JS question is,

"What happens if you do this?"

    var func = function func () {
        // blah
    };

jbrooksuk• 13 years ago

The function is able to reference itself, allowing recursion. This used to cause an error in Safari though, am I right?

aaronem23• 13 years ago

That doesn't seem special:

    var foo = function (n) { return foo(n); }; foo(1);

gives back "too much recursion", not "foo is not defined", in both Spidermonkey (Firefox 24) and V8 (node.js 0.10.something).

Aaronneyer• 13 years ago

A function can reference itself without defining the name twice. These both work just fine:

    var factorial1 = function(n) { return n < 1 ? 1 : n * factorial1(n-1) }
    
    function factorial2(n) { return n < 1 ? 1 : n * factorial2(n-1) }

hacknat5• 13 years ago

This is a bad FizzBuzz question, in my opinion.

solox33• 13 years ago

It's one of those questions that provoke the most thought, allow granular benchmarking of the interviewee's knowledge, and have a valid answer, in my opinion.

That is to say, this question has worked for us as a dev house, maybe not so much if you're hiring contractors, I can't say for sure.

aaronem23• 13 years ago

It looks to me like what happens is exactly what you'd expect, i.e., you end up with a function defined under the name "func", just as you would with any other function name. Is there something I'm missing?

xutopia• 13 years ago

There are two ways to define a function:

    var func = function(){};
    function func(){};

The example above is doing both at the same time... don't know if it's a mistake on their part or not.

However they're probably wondering if the user knows about scope and other such things. Inside the brackets we have a new scope but it has access to top level scope as well. They want to know that you know that stuff.

Try any of the two lines above in a js console (in browser) then type:

    window.func
    this.func
    func

The result should be the same.

sequoia3• 13 years ago

nothing? What answer are you looking for here? either a) there's something I'm totally missing or b) this is a really silly "trick" question.

3minus12• 13 years ago

It's a good chance to show off your knowledge of hoisting.

ShellfishMeme2• 13 years ago

The variable declaration is hoisted to the top, then is assigned a named function expression `func` so that `func.name === 'func'`. Useful for proper error messages and stack traces.

Something else I'm missing?

thomaslangston• 13 years ago

Could you go into more detail about why you would do A)

  var func = function func() { /* blah */ };

Instead of B)

  function func() { /* blah */ };

solox33• 13 years ago

Yeah, the average applicant says something along those lines. The top applicants also mention the IE bug associated with named function expressions: http://kangax.github.io/nfe/

3minus12• 13 years ago

Don't forget that the second func is unnecessary, unless it's a function that calls itself. Also it will show up as func when debugging instead of anonymous function.

yuchi2• 13 years ago

I teach JS. I use a a stronger one:

    var func = function func(func) {
      var func;
      console.log(typeof func);
    };
    function func(func) {
      console.log("func");
    }
    func("func");

thearn45• 13 years ago

Applied math/scientific computing:

If hiring someone, I would describe some practical scenarios problems involving the solution of finite-dimensional linear systems, and ask to see how they would suggest solving them in each circumstance (LU, QR, SVD, iterative methods, etc). More discussion oriented than in doing rote recital of algorithm structure, probably.

I would do something similar for functional characterization/pattern extraction via FFT/DCT/SVD/wavelets/ICA/etc.

Finally, I would construct some problems involving appropriate selection of statistical inference models and associated tests of hypothesis (from the usual the Fisher and Neyman-Pearson perspectives). The basics of Bayesian inference is good to know as well.

ColinWright9• 13 years ago

Interesting - this is exactly the kind of answer I'm looking to learn from. Are these really so utterly fundamental that someone could do them under pressure without thinking?

Is it the case that someone who can't answer these near automatically is, in effect, incompetent (in this field)?

I'm wondering if you've set the bar higher than FizzBuzz is in computing, or if this really is equivalent.

Thanks!

tel4• 13 years ago

I would agree with the op here. SVD in particular is so fundamental to the idea of data analysis I couldn't imagine talking to someone who even flinched at hearing it. Most other things fit at roughly the same level in my mind.

I feel like the mechanics of test selection biases against people who've specialized in Bayesian stuff—which might be very interesting! It's definitely a make-or-break kind of thing as to whether you can correctly formulate all the various moving parts and relate them correctly.

thearn45• 13 years ago

For this list, I'm basically assuming that I'm interviewing a candidate for a Ph.D. level (or equivalent) numerical analyst R&D type position. If they don't feel comfortable discussing the basics of these items, then they probably can't do too much more for us than algorithm plug&chug. Which has its value, but not what I had in mind.

That said, I also wouldn't expect someone to write out implementations on a whiteboard under pressure (I'm not a Google recruiter). I'd be more interested in prodding their brain to gauge their general level of understanding, which is (I'm pretty sure) how hiring committees for mathematicians in academia operate. If they have a good foundation, I think it's less important that they've rote memorized implementation details.

darkrho4• 13 years ago

Do you have any example problem to share? I've taken a numerical analysis class and this interview-like questions are appealing.

thearn45• 13 years ago

These are rough guidelines based on current best-practices that I know of, and shouldn't be treated as doctrine obviously. Numerical analysis/linear algebra is actually a pretty fast evolving field as far as applied math goes. Though statistics is a bit less dynamic at the moment, I'd say.

Honestly, after a certain amount of time, I'd expect a new hire would be able to teach me what is state-of-the-art in the field based on new literature.

But the questions I'd have in mind would be couched like this:

Linear system:

    - Is it small, square, and numerically well-conditioned? Use LU - it's pretty fast to write and pretty fast to use in practice.

    - Is it small, but rectangular (ie. overdetermined), or not as well conditioned? QR is a good choice.

    - Is it small, but terribly conditioned, or do you want to do rank revealing, or low-rank approximation while you're at it? Will you be using this matrix to solve many problems (multiple right-hand sides)? SVD would fit the bill

   - Is it large, or sparse, or implicitly-defined (ie. you don't actually have access to the elements of the matrix defining the system - you just have a surrogate function that gives you vectors in its range, or something)? Use an iterative algorithm. Krylov subspace methods (MINRES, GMRES, conjugate gradient, etc) are your friends here.

Pattern matching (more specific in question formulation):

    - If you wanted to determine the "strength" of a waveform (in a finite uniform sampling of data) that is re-occurring in a fairly regular way (like arterial pulse in an array of data taken from an oximeter), what type of transformation would you use, and how would you use the resulting information given in transform domain?

   - What if you wanted to determine the strength of a waveform that is short lived/impulse in nature, but re-occurs without any known periodicities (eg. eye blinks artifacts in a sample of EEG data)

   - How would your answers to the above questions change if there are n separate channels of data collected simultaneously (ie. sampled in different locations), which may be analyzed together?

Statistical analysis (might seem vague, I'd be more interested in good discussion with a candidate here than in actual whiteboard writing):

    - What does statistical significance mean, in the context of decision making? Is it a property of the test you perform, or is it a property of your data? (sort of a trick question, this basically rehashes the Fisher vs. Neyman & Pearson debates of the 20th century stats community)

   - Some cod problems of when to use z, t, f tests. Basically, you use them when your situation matches the appropriate inference models (two normally-distributed sample comparison of means with identical variances? t test.)

   - How do you construct an optimal test from scratch, if one doesn't already exist for your particular situation? (basically, if minimize type II error with fixed type I makes you comfortable for your problem, can you do use the Neyman-Pearson lemma to do likelihood ratio construction correctly)

   - What does a p-value actually mean? What if you instead wanted to have actual probabilities for your hypotheses, or you had apriori information that you wanted to use? (Bayesian inference is the winner here)

   - Probably something from point estimation: least squares, minimax criterion, Bayesian MAP estimates, general model fitting, those sort of thing. Brings it all back around to numerical (where I'm most comfortable). Like how applying statistical ridge regression is just knowing how to code up Tikhonov regularization, when you get down to implementation.

warech• 13 years ago

Not math but could be interesting anyway: Genomics, specifically quality engineering. When hiring for my team we ask candidates to generally describe 1) DNA translation and 2) statistics for experimental design (AQL, RQL, etc).

hacknat5• 13 years ago

I'm an SE now, but I got my degree in Northwest Semitic Literature and Linguistics:

Here's a couple:

Are Semitic languages VSO or SVO?

What does it mean that Semitic words are triliteral?

pliny• 13 years ago

SVO?

atroyn2• 13 years ago

Subject Verb Object.

Mvandenbergh• 13 years ago

Subject-Verb-Object word order like English or most other European languages. (I ate the apple).

Classical Arabic and other semitic languages are VSO, but spoken Arabic is mostly SVO.

ironchef• 13 years ago

Isn't the semitic language a gotcha because of how arabic and hebrew have changed to SVO (while remainder are largely vso?) Or is that the point of asking?

hacknat5• 13 years ago

In this case the assumption is that we're talking about ancient languages.

Edit

You're right that it would be (somewhat) impressive if they knew there was a transition.

tylerkahn• 13 years ago

Semitic words are triliteral:

http://en.wikipedia.org/wiki/Semitic_root

silvertonia• 13 years ago

A DBA I worked with had a good one-- just asked a question that was the textbook problem a left join solved.

jseliger2• 13 years ago

I do grant writing for nonprofit and public agencies. [1] I usually ask for a couple of major commas rules. Sometimes for semi-colon rules or for a description of passive voice. Chances are good that anyone who is zero for three isn't very good.

A lot of writers and would-be writers also have blogs; it only takes one to three paragraphs to figure out who can sling a coherent sentence and who can't.

Like FizzBuzz, being able to sling a coherent sentence doesn't mean that one can write a coherent 50-page document, but those who can't write a coherent sentence can't write a coherent 50-page document.

[1] Try http://blog.seliger.com if you're curious.

gjm114• 13 years ago

How well does the ability to write well correlate with the ability to articulate rules for writing well?

I'd have thought there are a lot of people who can write any quantity of text with impeccably placed commas (and semicolons, when the required tone permits them), but would freeze and stutter and gabble if asked for "a couple of major comma rules".

I'd put myself among their number, if only because it's not clear to me what sort of thing you mean by "comma rules". Descriptions of some situations where it is appropriate to use commas? "Commas are commonly used to separate items in a list when there are more than two such items" or "commas may be used, like this, to surround interpolations -- but for all but the shortest such interpolations you should consider using parentheses or dashes, or restructuring the sentence"? Descriptions of situations where it's inappropriate to use commas? "If you have two things that can function as separate sentences, don't separate them only with a comma; use a full stop or, in some contexts, a semicolon"? Or higher-level fuzzier principles? "Stops of all kind are placed to correspond roughly with pauses in speech and boundaries of grammatical units. The comma is the 'smallest' of stops, and is generally not used where the pause would be long or where the break in grammatical structure is great." Or what?

(I suspect a cultural difference at work here: I think formal analysis of grammar and punctuation may be a bigger deal in the US than it is in the UK.)

jseliger2• 13 years ago

How well does the ability to write well correlate with the ability to articulate rules for writing well?

The short answer is "pretty well." Usually I ask specifically for major comma rules, which I'd tend to define as:

* Connecting independent clauses with a conjunction * As part of a list * To offset a word or phase at the start of a sentence. * Like parentheses (or, in the lingo, an appositive phrase).

If they say, "I have no idea," that's a very bad sign; if they ask questions like yours, that's a good sign.

A fun, short book called Write Right! by Jan Venolia is worth reading if you're interested.

ecopoesis3• 13 years ago

I'm a software developer, but the code I work does a lot of DB access. I always ask a "two joins and an aggregate question."

Given three tables:

    authors     books       sales
    ----------  ----------  ----------
    id          id          id
    name        author_id   book_id
                title       date
                            price

find the total sales by author in November 2013. The result set should have two columns: author's name and their total sales.

aaronem23• 13 years ago

By "total sales", do you mean number sold or revenue?

lportion• 13 years ago

I wonder if that could be part of the assessment, to tell if the candidate is likely to verify uncertainties or make assumptions.

ecopoesis3• 13 years ago

I mean total revenue, but I leave it unspecified in the hope that someone will ask for clarification. Same with if they should include authors with no sales during the time period.

I like this question because the base query, however you interpret the unclear parts, is easy, but it still allows candidates to impress me by asking about the "edge" cases. And even if they just makes assumptions, I can still ask them to do the other versions to see if they really know what they're talking about. I'm always amazed at how many people can't convert an inner join to a left join, or can't change a sum() to a count().

codegeek• 13 years ago

I would make a couple of assumptions:

- price could be 0.0 for a book

- Total sales means the sum and not count

- Date format will be yyyymmdd (if not, assume that we converted in Oracle or Sybase)

    SELECT a.name, SUM(s.price) FROM authors a
    INNER JOIN books b ON (a.id=b.author_id)
    LEFT OUTER JOIN sales s ON (b.id = s.book_id)
    GROUP BY a.name
    HAVING (s.date >= '20131101' AND s.date <= '20131130')

zAy0LfpBZLC8mAC2• 13 years ago

s.date is not a group column and a.name seems like a bad PK

hdennis2• 13 years ago

Instead of the Left Outer Join, couldn't you also make it an Inner Join to S.BOOK_ID? The question, if I read it correctly, only requires you to return sales in Nov 2013. If there is no data for a book_id, you want to exclude it from your returned data, no?

seanalex2• 13 years ago

In SQL, this would be an issue due to the date column not existing in the group by. Additionally, because of the having statement, the left outer join is being treated as an inner join with respect to the results given.

Something like this could work (without going for an alternate approach such as Unions or sub-selects):

    SELECT a.name, ISNULL(SUM(s.price), 0.0) FROM authors a
    INNER JOIN books b ON (a.id=b.author_id)
    LEFT OUTER JOIN sales s ON (b.id = s.book_id)
    GROUP BY a.name, s.date
    HAVING (ISNULL(s.date, '20131101') >= '20131101' AND ISNULL(s.date, '20131101') <= '20131130')

Edit: Actually might be better to keep the null in the results like the original query. It's definitely better to know whether a book sold 1000 copies for $0.00 each or if no copies were sold.

hartleybrody• 13 years ago

My solution:

    SELECT authors.name, SUM(sales.price) FROM authors
      INNER JOIN books ON authors.id = books.author_id
      INNER JOIN sales ON books.id = sales.book_id
      WHERE sales.date >= Nov 2013 AND sales.date < Dec 2013
      GROUP BY authors.name

Although a coworker pointed out that inner joins would drop authors who haven't written books, and books that have no sales. If you want to include all of those, then use LEFT OUTER JOIN instead of INNER JOINs.

zAy0LfpBZLC8mAC2• 13 years ago

I think the fact that all solutions posted so far are broken and even repeat bugs I already pointed out validates this as a useful FizzBuzz test :-)

freehunter• 13 years ago

Information security. Our most basic interview demonstration question at my job is to hand the candidate a couple pages of tcpdump output and ask them to describe what was going on.

We don't use tcpdump all that often as we have more advanced tools, but if you can't understand a pretty raw representation of network traffic, you're probably not qualified to administer those advanced tools.

aegiso• 13 years ago

On/off producer + audio engineer. A good discriminator might be "it's squaring out; what do you do?". A good answer would lead to an argument about the compression war.

jcutrell• 13 years ago

10-20db cut in the lower freqs?

(Depends on what the source of the track is.)

golergka• 13 years ago

As a producer and non-native speaker, do you mean digital clipping?

minikomi• 13 years ago

As a chip tuner ... "What do you expect?" :)

retrogradeorbit• 13 years ago

How does it sound? You might want to leave it.

If you want to clean it up, drive the compressors/limiters less. ie. Turn the input trim down or turn compressor input gain down.

Another option is to open the compressors up. Take some (or all) of the compressors in the chain and halve their ratios.

A/B and compare.

crntaylor8• 13 years ago

I was a mathematician, and now work in finance (systematic trading). I've found a reasonable negative filter is

  A jar has 1000 coins, of which 999 are fair and 1 is double
  headed. Pick a coin at random, and toss it 10 times. Given
  that you see 10 heads, what is the probability that the next
  toss of that coin is also a head?

That tests their ability to turn a problem into mathematics, and some very basic conditional probability. Another common question (that I don't use myself) is to ask what happens to bond prices if interest rates go up.

thearn45• 13 years ago

The Monty Hall problem (or a subtle variant) is also great one to watch people work through. It's a chance to see if people can thing about probability in a sort of asymptotic way.

Basically (if they get stuck), ask them how they would choose if there were actually a 100 doors, but the same rules apply. Obviously, everyone switches. What about 99? 98? ... turns out, 3 doors is the smallest number where the strategy is optimal. But when the number is large, the answer is much more obvious.

crntaylor8• 13 years ago

The problem with asking Monty Hall in an interview is that ~75% of candidates already know the answer.

k2enemy• 13 years ago

The Tuesday boy problem is a little less known: http://mikeschiraldi.blogspot.com/2011/11/tuesday-boy-proble...

Guvante2• 13 years ago

Depressing, just asked my coworkers this and can't convince them it isn't an independent event :(.

alok-g2• 13 years ago

One issue I have with Monty Hall problem as an interview question is that the problem statement is too subtle, with several hidden assumptions. Interviewers often end up posing a different puzzle without realizing just by using a slightly different language to pose it.

jbermudes• 13 years ago

Should I parse it as tossing the same coin 10 times, or choosing from the jar 10 times?

crntaylor8• 13 years ago

Good question, and one that sometimes comes up when I ask it in interviews. You are tossing the same coin 10 times.

peteretep• 13 years ago

My wife and I have discussed this, and get a different answer to a few of the solutions we then googled for. I think it is as simple as: http://pastebin.com/gg5DTySG

pakitan• 13 years ago

I'm thinking this: http://pastebin.com/GW1hTXwD Dying to know if I made it through the math FizzBuzz :)

amalag• 13 years ago

This is the simplest explanation, thank you.

aeon10• 13 years ago

Do you mind posting a simple walkthrough for the answer

crntaylor8• 13 years ago

Sure. The slick answer is

The chance of picking the biased coin is 1/1000. The chance of seeing 10 heads from a fair coin is (1/2)^10 = 1/1024. These are nearly equal, so given that you've seen 10 heads, there is a 50/50 chance of having a biased coin. So the probability the next flip shows a head is

  P(H) = P(biased) * P(H|biased) + P(fair) * P(H|fair)
       = 0.75

The long answer -

Yo want to figure out P(biased | 10H). Using Bayes rule this is

  P(biased | 10H) = P(10H | biased) * P(biased) / P(10H)
                  = P(10H | biased) * P(biased) / (P(10H|biased) * P(biased) + P(10H|fair) * P(fair))
                  = 1 * (1/1000) / (1 * 1/1000 + 1/1024 * 999/1000)
                  ~ 0.5

and you now compute the probability of the next toss being a head as above.

drcode2• 13 years ago

Here's my walkthrough: http://pastebin.com/e2ea9XUD

jules9• 13 years ago

When we pick the coin, we have 1 in 1000 chance of getting the double heads coin, and 999 in 1000 chance of getting a fair coin. Lets call this P(fair) = 0.001, and P(fake) = 0.999.

When we have the double heads coin, the probability of getting 10 heads is 1: P(10 heads|fake) = 1. When we have a normal coin, the probability of getting 10 heads is P(10 heads|fair) = 0.5^10.

The quantity we want to compute is

    P(heads|10 heads) = P(fair|10 heads)*0.5 + P(fake|10 heads)*1 
                      = P(fair|10 heads)*0.5 + (1-P(fair|10 heads)) 
                      = 1 - P(fair|10 heads)*0.5.

To compute P(fair|10 heads) we use Bayes' rule:

    P(fair|10 heads) = P(10 heads|fair) * P(fair)/P(10 heads)

Here

    P(10 heads) = P(10 heads|fake)*P(fake) + P(10 heads|fair)*P(fair) 
                = 1*0.001 + 0.5^10*0.999.

We fill in the formula we got by Bayes' rule:

    P(fair|10 heads) = 0.5^10 * 0.999 / (1*0.001 + 0.5^10*0.999)

Then we fill in the original formula:

    P(heads|10 heads) = 1 - 0.5^10 * 0.999 / (1*0.001 + 0.5^10*0.999) * 0.5 
                      = 0.75308947108

madcaptenor2• 13 years ago

That's a nice filter. (Of course, I'm a former mathematician as well.) Here's how I think of it:

- the prior odds that you picked the double-headed coin are 1/999.

- after seeing ten heads, the posterior odds that you picked the double-headed coin are (2^10)/999 - let's approximate this as 1. (Bayes' theorem usually gets expressed in terms of probabilities, but it's so much simpler in terms of odds.)

- so it's roughly equally likely that you have the double-headed coin or any non-double-headed coin; the probability of flipping an eleventh head is then approximate (1/2)(1) + (1/2)(1/2) = 3/4.

110013• 13 years ago

0.7531 if you don't assume that 2^10 = 999

gallamine2• 13 years ago

Can you elaborate on the posterior calculation of (2^10)/999?

orp• 13 years ago

For the interested, some links to Bayes' theorem: http://en.wikipedia.org/wiki/Bayes'_theorem

http://yudkowsky.net/rational/bayes

Useful if you want to know (or need a good way to explain) what a posterior probability is and how it's different from a prior probability

phamilton2• 13 years ago

Why is it 1/999? Shouldn't it be 1/1000 since there are 1000 total coins?

kalid• 13 years ago

I vastly prefer Bayes Theorem as ratios vs. percentages (plug, wrote about it here: http://betterexplained.com/articles/understanding-bayes-theo...)

I like a "factor label" style approach where you can see the prior probability (Fair: Biased), the information about the flips, and the posterior probability (the revised chances after the new information is taken into account):

Prior * Information = Posterior

(Fair : Biased) * (10 Fair heads : Fair ) : (10 Biased heads : Biased) = 10 Fair Heads : 10 Biased Heads

Plugging in, we'd have:

(999 / 1) * (1 / 1024 ) / (1 / 1) = 999 / 1024

The odds are ever-slightly in favor of a biased coin. So we can mentally guess ever-slightly above 3/4 for the chance of another heads. We could write (999/2 + 1024) / (999 + 1024) on the whiteboard to be exact.

thejteam2• 13 years ago

I've used a similar question, but with two coins. I think if I am ever in a position where I am hiring again, I may follow-up that question with this extension to 100 coins.

What is the most common answer? Typically, I get either blank stares or a gut answer of just a little over 50%. I find that physics people are pretty good at solving the problem.

I would also REALLY hope that somebody who is applying for a job in finance understands the bond prices and interest rates, but I suppose that does make it a good fizz buzz type question.

crntaylor8• 13 years ago

I would also REALLY hope that somebody who is applying for a job in finance understands the bond prices and interest rates.

You'd be surprised at how many people can't answer instantly. Or how many people can't give a convincing description of what a share is, and what rights it gives you.

These are all easy questions, which to my mind is the point. The fact that someone can answer them doesn't tell you much, but if someone can't answer them then you need to think very hard about whether to hire them.

linuxlizard3• 13 years ago

mumble mumble bayes mumble mumble I'll show myself out.

danbmil993• 13 years ago

related problem:

a population has a 10% incidence of condition X. A test exists that is 90% accurate.

1) What is the expected percentage of positive test results? 2) if a person tests positive, what is the probability that they actually have the condition? 3) if a person tests negative, what is the probability that they are actually free of the condition?

JoshuaDavid• 13 years ago

By "90% accurate", you mean "10% false positive rate and 10% false negative rate", correct?

notahacker• 13 years ago

The bond prices question is a pretty bad filter, since it doesn't give the competent candidate much chance to express how they think, and a weak candidate has a good chance of guessing "they go down" and even a fair chance of blustering their way through followup questions/explanations.

On the flip side, you could probably unintentionally trip up someone with a generally competent grasp of economics/stats but a lack of specific interest in bonds over terminology if your followup questions start asking them to distinguish between types of yield.

Same with exchange rates (although I do remember back in school in a competitive presentation being complemented on my confident and plausible sounding explanation of the effect of an interest rate rise on exchange rates that also happened to be the reverse of the correct answer :-) )

ACow_Adonis3• 13 years ago

The funny thing is, I imagine I'd fail this, and a lot of other "interview" questions. (Not fizzbuzz incidentally :P)

Why? Because my brain just doesn't seem to work in the way people expect "experts" brains to work in our world of tests/qualifications.

Now for context, I don't consider my self some wishy washy "Oh I have a different KIND of intelligence" making-excuses dumb as nails nancy. I've worked several years now for my nation's statistics agency. I've written programs to calculate things professional statisticians couldn't (indeed that seems to be one of the reasons I get to keep my job :P) and just about every useless bloody stat there is, I've written my own probabilistic data linking software, finished in the top 10% of unrelated competitions on kaggle, and my formal qualifications are in economics. I don't think I'm the greatest thing ever, but if i might be so blunt, I feel I'm at the stage where I can confidently claim to have "proven my capabilities".

But I haven't memorized Bayes theorem (or any other probability or math-formulas), despite having applied it about 100 gazillion times. And despite being an economist, I haven't memorized "the relationship between bond prices and interest rates". Now, I could try to reason these things out from scratch in front of you, but I imagine most people in our world would see that as a "weakness" or trying to hide the fact that I couldn't answer the question.

With the probability one, I'd start going down the various interpretations of probability and whether your notion of probability is internally consistent/justified, etc etc etc. I doubt I could write the math on the white board of the top of my head in an interview (and i know several statisticians who couldn't also), but I could probably outperform most of the candidates who could in its application in the real world (speaking from experience), or be able to question whether there is a better tool for the job in the real world.

With the bond one, I know there's an answer that you expect me to give from rote during my education. But i won't. I haven't memorized it (because from experience, memorising these types of things is bad form, conditions you into erroneous thinking when they eventually turn out not to be universally true, and is far worse than reasoning, questioning or thinking about problems). So i'll ask you to describe your idea of a bond to me. I'll ask you to describe your idea of interest rates. Why are the interest rates rising? Maybe then, depending on what answers YOU give, I'll say "well then obviously bond prices must move inversely to interest rate movements", but there's just as much chance i'll pick up on some mistake you've made and never reach that point.

Now I'm not attacking you specifically. I don't know you, or what we think of each other, or how we'd interview each other. But from my experience, most people/recruiters/employers/interviewers would take my behaviour as a negative sign. A sign of "stalling" or "evading the question". Questioning, or reasoning, or skeptically interrogating things or mulling over questions for long periods of time, especially if they consider the answer "known", is a "bad sign".

And the rote learner, who'd just happened to memorise a particular formula or spent most of their time in one particular context, or bought the book on interview questions for said industry will get a big fat tick.

Moral of the story: Please don't use "interview questions" :P

baddox13• 13 years ago

What sorts of questions or tests were posed to you in interviews for jobs you ended up accepting? Or if you've never been in that situation, can you propose some interview techniques that would give the interviewer a good idea of your abilities?

ColinWright9• 13 years ago

So, to see if I understand you:

* The person suggesting the question says that this is trivial for people suited to the job in mind;

* You say you couldn't do this question;

* You also say that you would be suitable to do the job.

Given that the proposer of the question is the one that understands the job, I'm having a hard time understanding why you claim you would be suitable for it, given that you couldn't do the question. Please understand that I'm not attacking you specifically, I'm just having a hard time understanding your reasoning.

tripzilch2• 13 years ago

But from my experience, most people/recruiters/employers/interviewers would take my behaviour as a negative sign.

The negative sign is your stubborn conviction about the lack of value of rote memorization.

The stereotypical "rote learner" you describe in your before-last paragraph is just as one-sided as the opposite.

Of course neither extremes really exist and you probably have rote-memorized more things than you realize. You don't work out everything from scratch every time you encounter a medium hard problem.

Unless you actually do, in which case someone reasonably clever who does not stubbornly refuse to learn a few formulas will beat you by speed. Which is a reason to hire them over you.

That's the the point. You may be very smart and capable doing it this way, but learning a few basics (such as Bayes, in the context of statistics) doesn't really cost you anything. Memorizing a few things isn't hard. You won't actually run into problems like "erroneous thinking" because you're smart enough and knowing the conditions under which something holds is easy enough when you understand the thing. Additionally you get the knowledge when a particular important theorem does not hold, which is higher level knowledge that you just can't get when you reason from scratch every time (positive vs negative knowledge).

Memorizing a few of the basic important theorems and formulas in your field is such low-hanging fruit to improve yourself that a potential employer might ask why you're not doing it, even if you're so very capable without doing it.

Finally, there's communication with your peers. Maybe you can figure that stuff out by yourself easily, but when your colleagues say "ah, so we just use Bayes and poof", you'll be lagging behind figuring that out, and in reverse when you do these things from scratch, I'm assuming you'll be doing them much quicker, speeding through your ad hoc methods, leaving your team mates confused and wondering "why don't he just use Bayes?" (which may or may not be what you are in fact doing, but you lack the knowledge to tell them as much).

I'm sure you do a very good job at what you're doing now, the way you're doing it. I'm just pointing out that there are various well-justified reasons why employers can be wary of your refusal to memorize some basic field-knowledge, even when you're perfectly capable figuring out that stuff when you need it.

akalin• 13 years ago

Given that this is hacker news, I'm surprised that no one bothered to write a simulation to sanity-check their answer. Here's a quick and dirty one: http://jsfiddle.net/qc9qk/2/

The mistake that most people seem to be making is using P(biased) and P(fair) instead of P(biased|10 heads) and P(fair|10 heads).

Spoiler: The answer is ~0.75.

danbmil993• 13 years ago

with 1025 coins the numbers are nice:

1024/1025 * 1/1024 = 1/1025 (probability of unbiased coin, 10 heads) 1/1025 (probability of biased coin & 10 heads) relative probability = .5 the answer is then precisely 3/4

danso• 13 years ago

For news reporters, there's the AP Style test, which gives you text/headlines that you have to translate to the AP style, which is its own kind of grammar (e.g. for state abbreviations, Calif. instead of CA; always use [numerical-age]-[old] in describing ages: 15-year-old). It's a test more geared toward editors though.

In terms of reporting...there's no litmus test for how well you can report an event. The education beat, however, is pretty common for new reporters (it was my first), which is ironic considering how ridiculously complicated education is as a topic (same kind of financial/budgetary documents as any business, government bureaucracy, board politics, and of course, dealing with children)

martingoodson• 13 years ago

For a data scientist I ask "what's a p-value?" Both Junior and senior candidates often get this wrong. The only difference is that senior people bristle at such a simple question before also getting it wrong.

hnriot3• 13 years ago

It's always possible that if so many candidates get this wrong, especially senior ones that your understanding might be incomplete, or possible not understanding clearly. I often find that people get these pet questions and think they understand them when they don't really. I'm not even a data scientist or statistician and could tell you what a p-value is. I find it hard to believe experienced candidates can't.

dmd2• 13 years ago

Ok, now I'm confused, because I was under the impression that this is the first thing I ever learned in statistics - that a p value is how likely it is that a value created by chance would have been as extreme as the one the experiment gave. Is this wrong?

trthatcher• 13 years ago

You have the right idea.

You're assuming an underlying model for the data. You have a test statistic( that estimates a model parameter) and you have a hypothesis regarding a parameter. The p-value is the probability that you get a test statistic more extreme than the one observed assuming that your hypothesis is true.

Ex. You have a sample of 1000 men's heights. You compute the sample average height as 5'9 and a sample standard deviation of 3 inches.

(Unlikely) hypothesis: the average height is 4 feet. Your p-value is the probability of getting an sample average more extreme than 5'9 given that your 4 ft height hypothesis is true. Given that the sample standard deviation is 3 inches and 5'9 is 7 standard deviations from 4ft... the p-value is going to be small, so you'll reject that.

Note: I'm leaving out details and assumptions

tel4• 13 years ago

It's not wrong, but it did open up some great questions as to what it means to have values created by chance and how that relates to "this experiment".

thatthatis• 13 years ago

So what do you consider to be the/an appropriate answer to this question?

This seems like a case where "why do we use it," an "how do we use it correctly" are obvious but the definition of what it actually is is a complexity we covered once in freshman statistics and never needed again.

You don't hire a telemarketer by asking them "what is a telephone" you hire them by making sure they know how to use one correctly.

jkimmel• 13 years ago

I work in the life sciences. You would be amazed at what proportion of researchers have no conceptual understanding of what a p-value actually is.

sheetjs• 13 years ago

My Math "FizzBuzz" question is: prove Fermat's Little Theorem and Wilson's Theorem. Even those with very rudimentary understanding of modular arithmetic (coming from non-math backgrounds) can prove both with some pointers (obviously the process is interactive)

crntaylor8• 13 years ago

Interesting. I think the proof of Wilson's theorem is easy enough to be accessible for a non-mathematician - for non-prime n you can find a pair of numbers in the product (n-1)! that are congruent to 0 (mod n), and if n is prime then you pair up numbers in the product with their inverses until you are left with ±1.

But I can't think of a similarly low-level proof of Fermat's Little Theorem. Is there an obvious one I'm missing?

ColinWright9• 13 years ago

Consider Q to be the product (p-1)!. Then consider the product a.2a.3a.4a...(p-1)a. These are the same items rearranged, because a has an inverse.

But the product is also a^(p-1).(p-1)! by commutativity. So a^(p-1)=1 (mod p).

There's a clever idea in there, to consider prod(ka) for fixed a and k=1..(p-1). Not finding the clever idea means you won't prove it. Finding the clever idea is tricky. Once you know the clever idea the proof is trivial.

vvvVVVvvv• 13 years ago

Technical support analyst in the online advertising biz.

Our Fizzbuzz equivalent would be to mess with some HTML / JS and ask the interviewee to spot what's the issue. Or playing with a spreadsheet software to highlight stuff (pivot table, filters, duplicates, whatnot).

talmand5• 13 years ago

I build web sites. I would ask that the person complete a series of tasks that involved using Javascript to do a bit a typical DOM manipulations and CSS changes, especially using transitions and whatnot...

...without jQuery.

iron_ball• 13 years ago

Follow-up question: "Should you?"

tmcneal• 13 years ago

Just curious, why do you not allow the interviewee to use jQuery? Do you expect the candidate to know JavaScript's DOM-level APIs without having to look them up?

rimantas• 13 years ago

Native API are probably easier to learn, just more cumbersome to use :)

teebrz• 13 years ago

Hang out on forums, #javascript, etc some time and see how many people have problems because their understanding of the DOM begins and ends with the jQuery API. I see it all the time. I've seen big-name sites bug out or slow to a crawl because some dev wasn't thinking about what was going on behind their $()'s.

The DOM API isn't very large/complicated, and it shouldn't be hard to MOSTLY memorize it. It isn't a "gotcha" question though, a good interviewer is not gonna ding the heck out of you if your forget bits of it (most web devs do spend most of their time with jQuery, YUI, etc after all) - it's about whether you understand what's going on behind the scenes.

talmand5• 13 years ago

I don't mind the need to research DOM-level APIs on the fly. In fact, I'd be just as impressed that they not only know what they need to look up to refresh their memory, but where to look. Where and how they look might say things about them as well.

After all, I often have to look up a rarely used method. Seems unfair to judge harshly if they do so.

chime• 13 years ago

Why?

talmand5• 13 years ago

Because there are times that jQuery is not available to you for whatever reason. Most of time the tasks I stated are not really that hard to do in vanilla Javascript, it just can be more verbose as opposed to doing it with jQuery.

ecopoesis3• 13 years ago

Hah. I once asked an intern some random JS question and he used JQuery for everything. So I then asked him what the $ meant. That was a very awkward 5 minutes of silence.

run4_too4• 13 years ago

That's not really fizzbuzz, that's more the equivalent of asking a C programmer to write fizzbuzz in assembly (perhaps that's a little too strong a comparison, but you get the idea).

Fizzbuzz for websites would be to have someone code two paragraphs side by side with a header and footer in CSS.

talmand5• 13 years ago

If their primary task was to build HTML emails then I could understand that train of thought.

I suppose there are people out there that are working as front-end developers for websites that only work in HTML and CSS, but I would think that's getting more rare as time goes on. Of course, that could just be bias based on my own career.

But, going with your suggestion as a thought exercise, I would go in a different direction. To make a pattern like fizzbuzz I suppose I would do something more like: build a page with a series of paragraphs so that these CSS properties apply to every third paragraph, these CSS properties apply to every fifth paragraph, and so on. Something possible with CSS but requires the ability to think things through.

model-m• 13 years ago

When I teach calculus 1, I usually put a "high discrimination" question at the beginning of every exam. Student performance on that question is usually very well correlated with the exam grade. It helps me quickly assess class performance right at the start of the grading process.

Examples of such questions:

Draw the graph of a function f, continuous on the reals, such that: f(x) > 0 always, f'(x) < 0 always, and f''(x) always has the same sign as x.

The line y=3x-2 is tangent to the graph of y=f(x) at x=4. What is f'(4)?

zdw• 13 years ago

For sysadmin/ops jobs, I want to see debugging ability in addition to programming skill.

I usually ask about HTTP and DNS (for web-focused) or Kerberos/AD logins (for user focused).

There are a lot of moving parts to either of these, so a question like: "You type a web address into a browser, it doesn't load" can turn into questions about the DNS resolver process, system and network config, split horizon, time setup, etc.

Basically, I want to know if they have a grasp of how things all go together, and how to test the individual parts that make up the whole.

c0nsumer2• 13 years ago

More sysadmin / troubleshooter focused person here, and I love this sort of question. It also brings out people who will throw out things like "do a network capture". Then you either get the "well, send it to the network team!" answer or the (much more desirable) "look for X, Y, Z, or something weird in N...".

nulagrithom• 13 years ago

Are you saying "do a network capture" isn't desirable? It's not the first thing I would do, but I wouldn't get to Z before taking one.

X4• 13 years ago

These are questions I remember being asked. But they also asked what experience with servers I have and stuff..

     * At which layer things are in the OSI model.

     * How to reset AD user passwords.

     * What different kinds of servers are for.

     * Access port 25 in VLAN1 but not VLAN2 using port forwarding in the firewall

      * What ways of securing a DMZ are available in emergencies.

run4_too4• 13 years ago

"You type a web address into a browser, it doesn't load"

1) Check your internet connection. 2) Check if the website is broadcasting (assuming you control it).

99% of all instances of this issue solved right there. :-)

sbhere• 13 years ago

Imaging science. If I were hiring another imaging scientist:

Write your own Fourier Transform. [If your FizzBuzz questions involve actually writing/coding the FizzBuzz, I'd not request actually writing it...]

lp251• 13 years ago

I wonder how effective of a test this would be. Are the algorithmic & implementation details of the Fourier transform that important to imaging science? I would imagine that explaining the properties of the FT, it's connection to imaging modalities, etc would be far more relevant than actually coding a DFT.

How would you weight a naive implementation of the DFT vs the FFT?

0x09• 13 years ago

How would you weight a naive implementation of the DFT vs the FFT?

Luckily he didn't specify the dimensional requirements, so we can get away with f^[0] = f[0].

pawn9• 13 years ago

Where I work, we have a 4 question SQL test where we sit you in front of a dummy database, give you 4 printed results, and say "make the queries to produce exactly these results." Very very few people get all of them, but it gives us an idea of where somebody is at in their ability and knowledge.

The first is the easiest, and the second one isn't bad. The 3rd and 4th trip up most people though.

aaronem23• 13 years ago

I'd be curious to see that test.

pawn9• 13 years ago

Think you might be interested in applying? :-)

We're hiring...

RokStdy• 13 years ago

Ditto!

I'd love something like [0]You can't javascript under pressure, but You can't Query under pressure for SQL. :-)

[0]http://games.usvsth3m.com/javascript-under-pressure/

jtchang• 13 years ago

Can they look stuff up on the internet? A lot of queries require some ridiculous syntax like windowing in Postgres.

pawn9• 13 years ago

Yes, the full power of the internet is at your disposal. The catch is that you're limited to an hour to get it done.

abengoam• 13 years ago

I do a very similar thing at my job, but instead of showing the results I ask for a report such as "we want to get X,Y and Z for the Ws where P holds true".

barik• 13 years ago

This is an off-topic answer, but I see no reason why this thread shouldn't be generalized to FizzBuzz equivalents in other careers (in fact, it might be interesting to do so). Our electrical engineering FizzBuzz is an introductory, Freshman-level voltage drop problem, found within the first chapter of any Circuit Analysis textbook:

         R1  (N)  R2
  [VDD]-^^^^--*--^^^^----|

Given VDD, R1, and R2, compute the voltage at node N.

This works surprisingly well as a negative hiring filter. It's not intended to be a trick question at all: it can be solved with Ohm's Law:

  I = VDD / (R1 + R2)
  Vn = VDD - R1 * I

or faster and more intuitively using voltage dividers:

  Vn = VDD * R2 / (R1 + R2).

What's disappointing is that a large number of senior undergraduate students are unable to solve this problem -- which I think makes it a good EE equivalent of the FizzBuzz problem.

raverbashing3• 13 years ago

"What's disappointing is that a large number of senior undergraduate students are unable to solve this problem "

Ouch! :)

I'd say it's even simpler than a regular FizzBuzz.

aspensmonster• 13 years ago

What's disappointing is that a large number of senior undergraduate students are unable to solve this problem

...Wat? That's like, one of the easiest questions you could ever be asked. As a senior undergrad in his final semester for EE (Computer Engineering specialization), could you give me an idea of some of the more difficult questions you would ask?

n00bhere• 13 years ago

I was once given a boolean function, asked to implement it using logic gates. And then asked to optimize it based on a few criteria (for example: GNDs and VDDs cost a lot, reduce the gates, etc.)

The most annoying thing was, I was not expecting any gates related question so my optimizations were very... adhoc.

ColinWright9• 13 years ago

I hesitate to say this, because it might be misconstrued. However, some people seem not to know it, so it might be of value regardless ...

Once an item has more than 40 comments, if the number of comments is more than the number of points, there is a ranking penalty applied. This is because it's a good proxy fr an item being a flame-war.

So if you're interested in seeing more answers to this question, or carrying on the discussion, it's worth making sure you up-vote the item to try to avoid tripping the flame-war detector.

Of course, it may already be too late ...

larrys2• 13 years ago

Is it known whether the flame war detector applies any significance to particular words appearing in the comments to determine if there is actually any war going on just because there are not enough item up votes?

ColinWright9• 13 years ago

To the best of my knowledge it's purely depended on number of comments and number of points. There was a submission some time ago talking about all the factors involved in getting to, or not getting to, the front page.

I'll see if I can find it.

bentoner• 13 years ago

For poker, I see if they understand how squeezing works.

r-s• 13 years ago

when are you ever interviewing for a poker position?

I think that would be a good question though. Or even something simple like "Explain how you could set-up a polarized 3bet range".

smokey42• 13 years ago

My pet problem after FizzBuzz has been this for some time now:

    You are given a text in a file. Count all the words in the
    text and print out the words with their number of occurences
    in descending order.

This can be depressing at times.

ColinWright9• 13 years ago

Define "word". However, strings separated by space:

Print number of words:

    wc -w <filename>

Print words with counts in decreasing order:

    cat <filename>  \
    | gawk '{for (i=1;i<=NF;i++) print $i}' \
    | sort          \
    | uniq -c       \
    | sort -rn      \
    | less

There are optimizations to be made, but that would be my go to solution in the first instance.

agumonkey2• 13 years ago

This thread makes me feel like a worthless POS but at the same times motivates me to finish learning so many pending topics properly. Nothing's better than an actual test.

swartzrock• 13 years ago

A worthless POS would lack to motivation to finish learning...

agumonkey2• 13 years ago

I'm very low on motivation, but my derivative, even if small, is positive yes.

But I got a college (a good public one) diploma, yet reading this I feel anything above Linux devops and FizzBuzz would be far from my reach, that's what I meant by worthless P...

linuxlizard3• 13 years ago

Yeah. ITT all sorts of vocations I'm not even remotely qualified for but want to learn anyway.

ryanisinallofus• 13 years ago

If someone has UX on their resume I ask them to draw up a user flow diagram of getting groceries.

dxbydt2• 13 years ago

Based on interviews, POMDP has become a favorite FizzBuzz question for data scientists. So make sure you have a working example for that. I usually explain the tiger pot of gold in gruesome detail. https://www.google.com/search?q=tiger+pot+of+gold+pomdp

gallamine2• 13 years ago

Any recommendations for courses or books on Markov decision processes?

dxbydt2• 13 years ago

For whatever reason, pomdp has been co-opted by the AI community, so the books are pretty lousy and show-offy, often using nonstandard terms and newfangled jargon to explain what is really plain old probability theory with some state space transitions.Thrun's Probabilistic Robotics is the best one I could find. Any math professor can run circles around the material if it were treated as part of math instead of bringing AI into the mix.

aus_• 13 years ago

I just saw Wolf of Wall Street this weekend. Has anyone in sales been asked "sell me this pen" in an interview?

larrys2• 13 years ago

I'm good at sales.

But I would really bristle at being given a question like that (and luckily I don't have to interview so this will not happen).

For one think selling takes preparation, knowledge of the product and strategy. It also takes experience (for a particular product and buyer and situation). So in my mind I don't see what asking a question like that will prove other than that you can ad lib or bs in a way that doesn't matter.

Selling also takes interpreting cues (verbal and visual) from the potential buyer. With those cues you change strategy on the spot and try to hit the right hot buttons. [1]

In a hypothetical situation it's unlikely that those cues would be valid because the person you are trying to sell knows it's not a real situation.

[1] As an example the strategy that you would use to sell a car to a father for his daughter is not the same as to a middle aged woman. And by listening to the father you could tell what points are resonating and try to reinforce those points more if appropriate.

run4_too4• 13 years ago

This explanation actually properly answers the question, in my mind. :-)

chm2• 13 years ago

  A nation's newest war ship is slowly disappearing. The ship's hull
  is made of Aluminium while its cannon bores are made of Stainless Steel.
  What is happening, why, and how do you stop it?

Grad school chemistry/physics candicacy exam question, sure to generate colorful answers!

stevenrace• 13 years ago

'Galvanic corrosion' and applying a non-metalic layer between the cannon/deck would be my first thought. Now I'm curious as to some of the more 'colorful answers'.

chm2• 13 years ago

Yes indeed: two different metals in electrical contact through an electrolyte solution (sea water). One way to stop this is to use a sacrificial anode (where the oxidation occurs) made of Magnesium, although this would probably be unpractical in salt water. A colorful answer would be to replace the water with a fluid like 3M's Fluorinert and replace the air with a nitrogen atmosphere. But that would also be unpractical.

0xdeadbeefbabe• 13 years ago

My FizzBuzz equivalent: do they say date-uh or dat-ah.

jheriko• 13 years ago

Hi - vfx/games programmer here - I've never been given FizzBuzz - although similar problems generally appear on any programming test I've seen (reverse a string, find loop in linked list etc.) the better ones I've seen a couple of times now are:

"How do you reflect a vector about a normal? Name some uses."

"What is the dot product? Name some uses."

These aren't just filters but an experienced real-time rendering or physics programmer is going to have quite a lot to say about the practical implementations of either in particular situations and what hardware features are available to help you with them...

if there is a good theoretical understanding then they can talk a lot about what the dot product is, its relationship to matrix multiplication and tensor inner products in general. they can explain multiple approaches to the problem of reflecting the vector and derive their solutions from first principles instead of just repeating remembered knowledge.

there are lots of little domain specific bits of knowledge as well e.g. the reflection question can lead to discussion of the Blinn half angle approximation - why it works and why its no longer a particularly valid optimisation on today's hardware - the dot product question can lead to discussion of how to efficiently handle solving a quadratic equation on the GPU

really i expect a decent (games/vfx) programmer to run out of time whilst elaborating on answers to either of these questions (although not to the detriment of the rest of the test of course...).

the best filter is a strong demo though imo. never met a bad programmer who has a decent demo... none of the average, lazy or bad programmers i've worked with have one that i couldn't have crapped out in the evening before an interview.

linuxlizard3• 13 years ago

Embedded systems programming (firmware).

Explain the difference between interrupt context and thread context. (With Embedded Linux, also throw in kernel space and user space.)

FizzBuzz coding would be showing how to safely share information between interrupt and thread context. Would be listening for message queues, locking, interrupt enable/disable.

Also, if you have done a lot of programming, the term "race condition" should make the interviewee blanch in terror.

coreyoconnor2• 13 years ago

Quality Assurance (QA) engineer. I do QA Tools specifically but still need to be on top of most QA stuff. Other QA engineers exist in the company for in depth QA.

My initial question starts with: "build a function that takes a string and produces an integer". About 30% of candidates fail to get anywhere. 50% produce an incorrect implementation. 20% produce an implementation that is mostly correct. 9% produce an implementation that is mostly correct and well tested. 1% actually produce a complete and correct response. Which, as of right now, translates to exactly 1 candidate in 2 years. Who was rejected due to culture fit. A complete and correct answer is not required to pass the screen. ;-)

The reason this question is so effective is due to how the question is asked and the details of the solution. There is a lot more than just the initial problem statement. The full script assess: the candidates ability to determine requirements; ability to produce complete set of unit tests; ability to handle the boundary conditions.

There is a sharp division that occurs between QA engineers and non-QA engineers on the requirements gathering. All but 1 non-QA engineer I've interviewed assumed they had all the requirements before writing code. A clever solution is almost useless if it solves the wrong problem. Sometimes even worse than useless if the code adds a maintenance cost for no value.

Covering all the critical cases in testing is the next part that most candidates fail at. Even if the requirements they assumed are correct, none of the non-QA engineers have succeeded in writing a complete and good set of tests. Many add too many tests.

After those two the other parts are just seeing how close they can get to building the correct implementation. The candidates typically pass if they do well in all parts; perfection is not required. Still, I think it's interesting to note that almost nobody has ever written a 100% correct solution. Even if they are given all the requirements in detail.

This question does not asses algorithm design ability. At all really. Well, I suppose there was somebody who immediately proposed "binary search!" and really wanted to stick with that idea. No clue why...

collyw• 13 years ago

This would match your specification.

    def string_to_int(str):
        
        return 1

coreyoconnor2• 13 years ago

That would match the initial specification. The point is for the candidate to note that the initial specification is too ambiguous and determine what they do about it.

If they gave that answer and then said "which is why the specification is weak" then great! If they gave that answer and called it done... well... not so good.

Ask HN: What's your speciality, and what's your "FizzBuzz" equivalent?

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