Comment On More Limitin', Wrong Major, and Parallel Universe Replacement

Mathlete :

This is just plain wrong.

Anchors aweigh:

The question usually assumes a balance scale (at least for the 8 weight issue).

For that:
1) Weigh A+B+C vs D+E+F. If they are equal then G or H are heavier.
2) If G or H are heavier, then obviously weigh them against each other.
3) If G and H are the same, then repeat the step one with the heavier triad, but leaving one out.

So 2 weighings for 8 on a balance scale.

Paddy Ryan:

The real tricky one is 12 in 3 balances (all outcomes covered)

Cishuman:

The first one is just wrong. After all, HTML + CSS is Turing Complete, and therefore it is in principle possible to write a Java interpreter in it...

dkf:

It goes something like this: You've got a box with a bunch of lights in it, one of which is broken. The box is opaque and openable; a switch in the hinge mechanism ensures that no electricity is flowing through the circuit when the lid is open. How do you work out which light is broken so you can fit the replacement?

The answer's obvious and trivial to remember once you know it; it's a stupid “A-ha!” question that reveals that the interviewer isn't very good at it. A good interview question should be either genuinely tricky or thoroughly open-ended; in the former case, you're testing whether they actually know what they claim, and in the latter case you'd be looking for whether the interviewee identifies the major strategies for tackling the problem.

this socks:

dkf:

It goes something like this: You've got a box with a bunch of lights in it, one of which is broken. The box is opaque and openable; a switch in the hinge mechanism ensures that no electricity is flowing through the circuit when the lid is open. How do you work out which light is broken so you can fit the replacement?

The answer's obvious and trivial to remember once you know it; it's a stupid “A-ha!” question that reveals that the interviewer isn't very good at it. A good interview question should be either genuinely tricky or thoroughly open-ended; in the former case, you're testing whether they actually know what they claim, and in the latter case you'd be looking for whether the interviewee identifies the major strategies for tackling the problem.

The only correct answer is: "Don't replace the lightbulb, it's inside a box and completly useless. Why change it?"
Think outside the box.

dkf:

The poop of DOOM:

I never actually heard the lightbulbs thing. How does that one go?

It goes something like this: You've got a box with a bunch of lights in it, one of which is broken. The box is opaque and openable; a switch in the hinge mechanism ensures that no electricity is flowing through the circuit when the lid is open. How do you work out which light is broken so you can fit the replacement?

Tarl:

I assume this is an important problem because you are selling live chickens from your farm in Ye Olde Common Marketplace for 12 Copper Tarsks each, and you suspect the Warrior in front of you (smartly equipped with red tunic and steel sword) is attempting to defraud you by sneaking in one Copper Tarsk that has been slightly shaved around the edges.

Peter:

Tarl:

I assume this is an important problem because you are selling live chickens from your farm in Ye Olde Common Marketplace for 12 Copper Tarsks each, and you suspect the Warrior in front of you (smartly equipped with red tunic and steel sword) is attempting to defraud you by sneaking in one Copper Tarsk that has been slightly shaved around the edges.

Tarl? Would that be Tarl Cabot, Tarnsman of Gor?

Oh God, I'm so embarrassed that I caught the reference...

Puzzles:

Whenever I see someone bring up that lightbulb puzzle, I feel compelled to point out that the puzzle itself is fundamentally broken.

The normal assumption in a puzzle is that all the components are ideal, because the story is really just window-dressing on an ABSTRACT puzzle. If something is in an opaque box, you can't peek through a crack. If something has an on/off switch, you can't hold it in some middle position that makes intermittent contact. If you don't make those kinds of assumptions, these puzzles generally have a huge number of possible solutions, most of which are uninteresting and rely on circumstances not specified in the problem statement.

The accepted solution of the lightbulb puzzle is to check the temperature of the bulbs. But that relies on an arbitrary non-ideal assumption (non-negligible waste heat) that isn't stated in the problem, so that's no more legitimate an answer than "I peek through a crack in the box" or "I trace the wires to see what's connected to what". It's arguably not even a REASONABLE assumption these days--what if the lights are LEDs?

Lateral thinking puzzles don't generally belong in interviews, but that particular puzzle doesn't even belong in a game of puzzles. If you got the "correct" answer without being told, that actually means you're WORSE at these puzzles than many of the people who didn't get it, because under the normal implicit rules, it doesn't have a solution.

clcto:

5 weights in 3 weighings? That doesn't require any level of brain power. Isn't the question 8 in 2 weighings?

I imagine that puzzle has many permutations depending on the exact nature of the measurement tool you use and whether you are told in advance that the different weight is lighter or heavier or only that it is "different".

8 is likely a popular number because it is a power of 2, and therefore adds an extra red herring to the puzzle.

MrBester:

Then you get to look in the box and marvel at the stupidity ad pointlessness of making an opaque box containing light bulbs that can be switched on when the box is closed.

this socks:

dkf:

It goes something like this: You've got a box with a bunch of lights in it, one of which is broken. The box is opaque and openable; a switch in the hinge mechanism ensures that no electricity is flowing through the circuit when the lid is open. How do you work out which light is broken so you can fit the replacement?

The answer's obvious and trivial to remember once you know it; it's a stupid “A-ha!” question that reveals that the interviewer isn't very good at it. A good interview question should be either genuinely tricky or thoroughly open-ended; in the former case, you're testing whether they actually know what they claim, and in the latter case you'd be looking for whether the interviewee identifies the major strategies for tackling the problem.

The only correct answer is: "Don't replace the lightbulb, it's inside a box and completly useless. Why change it?"
Think outside the box.

airdrik:

geoffrey:

Puzzles:

Whenever I see someone bring up that lightbulb puzzle, I feel compelled to point out that the puzzle itself is fundamentally broken.
...

The point of the light bulb puzzle is that it is best to go down the path of least resistance first. Maybe the bulbs do not put out heat, but given that most do, it is an option with a high probability of success.

I'm more interested in someone who will troubleshoot through experimentation and observation, and who will not be more interested in the elegance or cleverness of the solution than in solving the problem at hand.

It is still a fundamentally broken puzzle - it relies on assumptions about particular light bulbs (yes the most common type, but alternatives are readily available and that common type is approaching a rapid decline). While most candidates will have had some experience with a heated bulb (who hasn't changed a light bulb just after turning it off, or tried while it was still on), slim few are going to make the required leap to the assumption made by the puzzle to make it solvable.

There are plenty of other puzzles which don't have some catch to them from which the puzzle draws assumptions and requires familiarity with the catch to solve.

geoffrey:

The point of the light bulb puzzle is that it is best to go down the path of least resistance first. Maybe the bulbs do not put out heat, but given that most do, it is an option with a high probability of success.

QJo:

One is almost tempted to say to the interviewer: "In such a set of circumstances, I would ask myself: What would Jesus do?"

boog:

Q: Why are manhole covers round?

Cishuman:

Eh, just change all light bulbs. The beancounters will complain about the cost, but who cares about that, amiright?

Rootbeer:

if one of the lamps has stopped working, then cookies are ruined and the company loses money.

Herby:

Puzzles...
One time when I was in an airport lounge, I noticed a math teacher giving quizzes to his group of students. Being the helpful type, I answered them before he could get the whole puzzle out. It felt real good for me (a bystander) and you could see the math teacher fuming that I knew the answers.
The two puzzles were:
You have a bunch of socks in a drawer, (usually 10 black, and 10 brown), how many socks does it take to get a proper pair to wear. Answer: 3.
A tree is dropping leaves as the season progresses. Each day it drops twice as many as the day before. Assuming that it always drops the maximum numbe, on which day do most of the leaves drop. Answer: last day.

I was smiling as I went to the plane.

Rootbeer:

But let's say for argument's sake that it's part of an industrial cookie-making machine. The uncooked rounds of dough travel along a conveyor belt, where they are cooked to a perfect golden brown by a gauntlet of infrared lamps; if one of the lamps has stopped working, then cookies are ruined and the company loses money. ...
Opening the box to determine which lamp has malfunctioned requires the entire line to be shut down, which also costs the company money, explaining the restriction that the box can only be opened and observed once.

trtrwtf:

Rootbeer:

But let's say for argument's sake that it's part of an industrial cookie-making machine. The uncooked rounds of dough travel along a conveyor belt, where they are cooked to a perfect golden brown by a gauntlet of infrared lamps; if one of the lamps has stopped working, then cookies are ruined and the company loses money. ...
Opening the box to determine which lamp has malfunctioned requires the entire line to be shut down, which also costs the company money, explaining the restriction that the box can only be opened and observed once.

If one of the bulbs has gone on strike, then fire any idiot who's running the machine and wasting cookie dough while the machine is not working.
Then fire the maintenance guy who's apparently sitting on his thumbs instead of fixing the damned busted bulb by opening the box and turning on the switches until he finds the busted one.
And then re-hire him and fire him again for not having an effective schedule for bulb replacement. These bulbs should be replaced before they hit expected end-of-life, not after they fail.
Then fire everyone in the place and outsource the thing to Hyderabad and ship the cookies back to the states.

Nagesh, we have work for you!

Nagesh:

trtrwtf:

Rootbeer:

But let's say for argument's sake that it's part of an industrial cookie-making machine. The uncooked rounds of dough travel along a conveyor belt, where they are cooked to a perfect golden brown by a gauntlet of infrared lamps; if one of the lamps has stopped working, then cookies are ruined and the company loses money. ...
Opening the box to determine which lamp has malfunctioned requires the entire line to be shut down, which also costs the company money, explaining the restriction that the box can only be opened and observed once.

If one of the bulbs has gone on strike, then fire any idiot who's running the machine and wasting cookie dough while the machine is not working.
Then fire the maintenance guy who's apparently sitting on his thumbs instead of fixing the damned busted bulb by opening the box and turning on the switches until he finds the busted one.
And then re-hire him and fire him again for not having an effective schedule for bulb replacement. These bulbs should be replaced before they hit expected end-of-life, not after they fail.
Then fire everyone in the place and outsource the thing to Hyderabad and ship the cookies back to the states.

Nagesh, we have work for you!

Your atitude is very demeening. Sorry!

Mastur Plan Software:

boog:

Q: Why are manhole covers round?

I prefer my manholes uncovered.

What was his favorite project to work on? "Uhh, they're'll'bout the same."

boog:

Mastur Plan Software:

boog:

Q: Why are manhole covers round?

I prefer my manholes uncovered.

Another discomforting answer - just be sure to wink at the interviewer, for added hilarity.

A Gould:

geoffrey:

The point of the light bulb puzzle is that it is best to go down the path of least resistance first. Maybe the bulbs do not put out heat, but given that most do, it is an option with a high probability of success.

That's an assumption that is only going to get worse, and it begs the question - if you're giving me physical access to the bulbs and the switches, why don't I have access to the wiring?

It's also a question that assumes that you're willing to play with electricity with no gear. Always wondered why this would be considered a desirable trait, considering how high Worker's Comp premiums can go...

geoffrey:

A Gould:

geoffrey:

The point of the light bulb puzzle is that it is best to go down the path of least resistance first. Maybe the bulbs do not put out heat, but given that most do, it is an option with a high probability of success.

That's an assumption that is only going to get worse, and it begs the question - if you're giving me physical access to the bulbs and the switches, why don't I have access to the wiring?

It's also a question that assumes that you're willing to play with electricity with no gear. Always wondered why this would be considered a desirable trait, considering how high Worker's Comp premiums can go...

Why you don't have access to the wiring is irrelevant. You do not get to dictate the conditions under which you can solve a problem.

This quiz weeds out the bystanders from the go-getters. Case in point.

Mastur Plan Software:

I would grab as many socks as possible.

Also, I may be suffering from "puppeteer's bias".

not frits at all:

What was his favorite project to work on? "Uhh, they're'll'bout the same."

Well, I had a "friend" who was afflicted with advanced indecision disorder, and let me assure you that either:
a) It is no laughing matter
b) It is funny as hell
c) I don't remember

Decide for yourself.

Mr Zip:

Herby:

Puzzles...
One time when I was in an airport lounge, I noticed a math teacher giving quizzes to his group of students. Being the helpful type, I answered them before he could get the whole puzzle out. It felt real good for me (a bystander) and you could see the math teacher fuming that I knew the answers.
The two puzzles were:
You have a bunch of socks in a drawer, (usually 10 black, and 10 brown), how many socks does it take to get a proper pair to wear. Answer: 3.
A tree is dropping leaves as the season progresses. Each day it drops twice as many as the day before. Assuming that it always drops the maximum numbe, on which day do most of the leaves drop. Answer: last day.

I was smiling as I went to the plane.

What if my tree has 1025 leaves? You need to give me a probability distribution of leaf counts in the population of trees to be able to assess whether the most leaves drop on the last day or second to last day.

Puzzles:

Whenever I see someone bring up that lightbulb puzzle, I feel compelled to point out that the puzzle itself is fundamentally broken.

The normal assumption in a puzzle is that all the components are ideal, because the story is really just window-dressing on an ABSTRACT puzzle. If something is in an opaque box, you can't peek through a crack. If something has an on/off switch, you can't hold it in some middle position that makes intermittent contact. If you don't make those kinds of assumptions, these puzzles generally have a huge number of possible solutions, most of which are uninteresting and rely on circumstances not specified in the problem statement.

The accepted solution of the lightbulb puzzle is to check the temperature of the bulbs. But that relies on an arbitrary non-ideal assumption (non-negligible waste heat) that isn't stated in the problem, so that's no more legitimate an answer than "I peek through a crack in the box" or "I trace the wires to see what's connected to what". It's arguably not even a REASONABLE assumption these days--what if the lights are LEDs?

Lateral thinking puzzles don't generally belong in interviews, but that particular puzzle doesn't even belong in a game of puzzles. If you got the "correct" answer without being told, that actually means you're WORSE at these puzzles than many of the people who didn't get it, because under the normal implicit rules, it doesn't have a solution.

clcto:

5 weights in 3 weighings? That doesn't require any level of brain power. Isn't the question 8 in 2 weighings?

I imagine that puzzle has many permutations depending on the exact nature of the measurement tool you use and whether you are told in advance that the different weight is lighter or heavier or only that it is "different".

8 is likely a popular number because it is a power of 2, and therefore adds an extra red herring to the puzzle.

trtrwtf:

And then re-hire him and fire him again for not having an effective schedule for bulb replacement. These bulbs should be replaced before they hit expected end-of-life, not after they fail.

Cantabrigian:

The puzzle says "Each day it drops twice as many as the day before", so the number of leaves on the tree must be of the form k(2^n - 1). (Strictly speaking there is no solution: the first day that any leaves fall fails to satisfy the condition.)

2*0 = 0

pjt33:

trtrwtf:

And then re-hire him and fire him again for not having an effective schedule for bulb replacement. These bulbs should be replaced before they hit expected end-of-life, not after they fail.

You missed the step where you verify that the bulbs didn't fail before the expected end-of-life.

trtrwtf:

I don't care about that. I'm not firing him for bulbs failing, I'm firing him for not having a bulb replacement schedule. If he had a bulb replacement schedule, I'll fire him for something else. I don't like that guy. I don't like the cut of his jib, if you know what I mean.

Behold My Final Form! Zunesis!:

Now we see the true purpose of "rules": a means of establishing arbitrary authority to get rid of people you don't like.

Jellineck:

Lucent:

VeryBestDeveloperNumber1:

Mmm, racism:

LOL, it's funny because he has an accent!

Racism, huh? I don't think I saw any mention of the interviewee's race. But yes, it's funny because he has an accent.

No it's definitely racist because that's the way black people talk!

I'm not sure he is black. He said "jarva", not purkles.

Nagesh:

boog:

Mastur Plan Software:

boog:

Q: Why are manhole covers round?

I prefer my manholes uncovered.

Another discomforting answer - just be sure to wink at the interviewer, for added hilarity.

Manhole cover is round because the mold to make them is round. If mold to meke them is square, then you can have square or rectangle or any shape you like.

chic:

mjk340:

TRWTF is an ORA-1555 error

TRWTF is asking about an error number in an interview.

boog:

QJo:

One is almost tempted to say to the interviewer: "In such a set of circumstances, I would ask myself: What would Jesus do?"

That ought to change the subject! On that note:

Q: Why are manhole covers round?
A: Because God made them that way.