Live data from Hacker News

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

news.ycombinator.com

261–270 of 363 posts

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

#261

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 p…

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

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

#262

Earlier quoted context omitted.

The probability of which coin you have affects the probability of the next toss coming up heads, so having this knowledge is implicit in determining the solution.

That probability was determined the moment you picked the coin out of the jar. It makes no difference what you do to it after the pick. Hold it in your hand for a day, flip it 10 times, sit on it, whatever - the end result is that p(heads) for that particular coin has not changed . p(heads) will be either 0.5 for a real coin or 1.0 for the rigged one. The probability then comes down to what coin you picked at the sta…

OK, What if I flipped it 10,000,000 times and got all heads? What is the probability that I have the non-fair coin? What is the probability for the next toss?

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

#263

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

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".

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

#264

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

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".

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

#265

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

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".

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

#266
post #176

Earlier quoted context omitted.

Ask yourself a question: can you use the data (the 10 coin tosses) to update the probability of the current coin being two-headed?

I wouldn't use the data. The coin hasn't changed since I picked it out of the jar. If I flip it 1, 10, or 10e100 times, the coin would still be the same coin. So figure the p(heads) for the coin and ignore the previous history. Overthinking it is why this makes a good FizzBuzz problem.

Let's consider that it might be a fair coin, or it might be a double-headed coin.

Let's also say that every time you flip the coin and it comes up tails, you win $5. And every time you flip the coin and it comes up heads, you lose $1.

Clearly, this would be a great game to have the opportunity to play, if the coin is fair. Every time you flip you either win $5 or lose $1, so your profit, on average, is $4 per flip.

You've flipped it 10 times so far, and it's come up heads every time, and you've lost $10.

After you're $10, $100, $1000, or $10e100 in the red, without ever seeing a win, when do you change your mind about playing this game?

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

#267
post #176

Earlier quoted context omitted.

Ask yourself a question: can you use the data (the 10 coin tosses) to update the probability of the current coin being two-headed?

I wouldn't use the data. The coin hasn't changed since I picked it out of the jar. If I flip it 1, 10, or 10e100 times, the coin would still be the same coin. So figure the p(heads) for the coin and ignore the previous history. Overthinking it is why this makes a good FizzBuzz problem.

Yes, it's still the same coin, but you don't know which coin you got. You know that you got 10 consecutive heads though. How improbable this is if you got a fair coin? How probable this is with the double-head coin? This is the data you can use to update the probability.

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

#268
post #74

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.

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

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.

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

#269
post #113

Earlier quoted context omitted.

Think you might be interested in applying? :-) We're hiring...

I'm always interested in applying :-)

Send me your resume and I'll make sure it gets into the right hands. For the purposes of this comment thread, my email address is heresmyresume@viewthesource.org

(I catch anything sent to viewthesource.org, so I like to customize it when giving my email to people)

It should be noted that we're in Bentonville, AR. That could potentially be a limiting factor for some people.

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

#270

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 p…

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?

Post reply on HN