Comment On Job Interview 2.0: Now With Riddles!

Saladin:

Quick. Given eight quarters -- one weighing more or less than the rest -- and a balance scale, if you were faced with the task of figuring out which was the odd coin out using the fewest weighings possible, what would you do?

Obviously, I pocket the quarters and leave this stupid interview, giving me enough change to buy a Coke and pay the highway toll on the way to my next (hopefully better) job interview.

Anonymous Coward:

Bit of an ax to grind, much? The WTF is good (a proper answer to a rather silly question), but the general assertion that brainteasers are worthless is silly. Obviously, there will be some people who suck at brainteasers who are great programmers, just as there are some people who flunked out of college who are great programmers, but it's still a valid item of interest. Anything that measures lateral thinking and makes interviews with soulless corporations a little more fun is a good thing in my book.

Rodyland:

- You've got a chicken, a fox, and a bag of grain on one side of the river, and a boat that holds you and one of the chicken/fox/grain. If the fox is left alone with the chicken, he'll eat it. If the chicken is left alone with the grain, he'll eat it. How do you get all across the river so that nobody/nothing gets eaten.

Rodyland:

- You have a 3 litre jug and a 5 litre jug. How do you get exactly 4 litres into the 5 litre jug?

Rodyland:

- Why are manhole covers usually round?

Rodyland:

- You've got a chicken, a fox, and a bag of grain on one side of the river, and a boat that holds you and one of the chicken/fox/grain. If the fox is left alone with the chicken, he'll eat it. If the chicken is left alone with the grain, he'll eat it. How do you get all across the river so that nobody/nothing gets eaten.

vt_mruhlin:

Saladin:

Quick. Given eight quarters -- one weighing more or less than the rest -- and a balance scale, if you were faced with the task of figuring out which was the odd coin out using the fewest weighings possible, what would you do?

Obviously, I pocket the quarters and leave this stupid interview, giving me enough change to buy a Coke and pay the highway toll on the way to my next (hopefully better) job interview.

I actually saw a good discussion of this one, and how that particular example can be used to guage programming skills. Correct solution was to do a binary sort on on. Put 4 coins on each side of the scale, discard the lighter half, weigh the remaining 4, then weigh the remaining two.....

Course the person who answers that correctly probably just heard it before. Nobody thinks about weighing quarters that fast.

Grandpa:

Three players enter a room and a red or blue hat is placed on each person's head. The color of each hat is determined by a coin toss, with the outcome of one coin toss having no effect on the others. Each person can see the other players' hats but not his own.

No communication of any sort is allowed, except for an initial strategy session before the game begins. Once they have had a chance to look at the other hats, the players must simultaneously guess the color of their own hats or pass. The group shares a hypothetical $3 million prize if at least one player guesses correctly and no players guess incorrectly.

What strategy would you use?

Adam Z:

Everyone should guess the same color. Statistically, at least one hat would be that color in a group of 3 or more.

captcha: wigwam
Although flim flam is more appropriate for the topic

Anonymous Coward:

Grandpa's puzzle sounds like a trick. The color of your hat is independent from the color of the other hats, so seeing the other hats gives you no information. It's possible that order of guessing / passing could be used to offer information, but that's been ruled out as well by the fact that everyone has to go simultaneously with no communication. So, basically, you've been given useless information and are stuck with no better than a guess. Pick one person and have them guess wildly while the others pass, you have a 50% shot.

Eggtastic:

One problem is that these brain teasers do not test lateral thinking or problem solving skills. They test whether someone has read the same book of brain teasers. If the interviewer were inventing completely original brainteasers, they might possibly show an aptitude for original thought (but more likely the luck to identify some unusual trick having no application outside the specific brain teaser), but I sincerely doubt anyone is doing so. Instead, they pull a bunch from a favorite source. Those who recognize them and can put on a good show of pretending they are solving them for the first time look like geniuses. Those who do not, may or may not figure out the right trick fast enough to impress the interview. Not a terribly useful test.

vt_mruhlin:

Saladin:

Quick. Given eight quarters -- one weighing more or less than the rest -- and a balance scale, if you were faced with the task of figuring out which was the odd coin out using the fewest weighings possible, what would you do?

I actually saw a good discussion of this one, and how that particular example can be used to guage programming skills. Correct solution was to do a binary sort on on. Put 4 coins on each side of the scale, discard the lighter half, weigh the remaining 4, then weigh the remaining two.....

Zoe:

The hat one is easy. Just call out the colour of the hat to your left ( or right, as long as everyone picks the same direction ). The chance of having two hats in sequence in this problem is 100%.

vt_mruhlin:

I actually saw a good discussion of this one, and how that particular example can be used to guage programming skills. Correct solution was to do a binary sort on on. Put 4 coins on each side of the scale, discard the lighter half, weigh the remaining 4, then weigh the remaining two.....

- You've got a chicken, a fox, and a bag of grain on one side of the river, and a boat that holds you and one of the chicken/fox/grain. If the fox is left alone with the chicken, he'll eat it. If the chicken is left alone with the grain, he'll eat it. How do you get all across the river so that nobody/nothing gets eaten.

Tarwn:

Hat Problem:
Why is everyone guessing, thats silly.

There are only two color hats. In the initial strategy session have everyone agree to point at red hats.

Everyone then gets a random hat, hands are raised to point only at members wearing red hats, everyone knows the color they are wearing (either they are being pointed at or they aren't), no guessing required.


This of course assumes that one of the members isn't a complete jackass willing to pass up on his/her portion of $3 million just to see the reactions of the other two members.

Anon:

Still, I'd give bonus points for using the term "binary sort".

Grandpa:

No communication of any sort is allowed, except for an initial strategy session before the game begins.

Once they have had a chance to look at the other hats, the players must simultaneously guess the color of their own hats or pass. The group shares a hypothetical $3 million prize if at least one player guesses correctly and no players guess incorrectly.

What strategy would you use?

Eggtastic:

Anonymous Coward:

Bit of an ax to grind, much? The WTF is good (a proper answer to a rather silly question), but the general assertion that brainteasers are worthless is silly. Obviously, there will be some people who suck at brainteasers who are great programmers, just as there are some people who flunked out of college who are great programmers, but it's still a valid item of interest. Anything that measures lateral thinking and makes interviews with soulless corporations a little more fun is a good thing in my book.

One problem is that these brain teasers do not test lateral thinking or problem solving skills. They test whether someone has read the same book of brain teasers. If the interviewer were inventing completely original brainteasers, they might possibly show an aptitude for original thought (but more likely the luck to identify some unusual trick having no application outside the specific brain teaser), but I sincerely doubt anyone is doing so. Instead, they pull a bunch from a favorite source. Those who recognize them and can put on a good show of pretending they are solving them for the first time look like geniuses. Those who do not, may or may not figure out the right trick fast enough to impress the interview. Not a terribly useful test.

Harvey:

Rodyland:

- You've got a chicken, a fox, and a bag of grain on one side of the river, and a boat that holds you and one of the chicken/fox/grain. If the fox is left alone with the chicken, he'll eat it. If the chicken is left alone with the grain, he'll eat it. How do you get all across the river so that nobody/nothing gets eaten.

First, shoot the fox...

Eggtastic:

vt_mruhlin:

Saladin:

Quick. Given eight quarters -- one weighing more or less than the rest -- and a balance scale, if you were faced with the task of figuring out which was the odd coin out using the fewest weighings possible, what would you do?

Obviously, I pocket the quarters and leave this stupid interview, giving me enough change to buy a Coke and pay the highway toll on the way to my next (hopefully better) job interview.

I actually saw a good discussion of this one, and how that particular example can be used to guage programming skills. Correct solution was to do a binary sort on on. Put 4 coins on each side of the scale, discard the lighter half, weigh the remaining 4, then weigh the remaining two.....

Course the person who answers that correctly probably just heard it before. Nobody thinks about weighing quarters that fast.

And yet the solution you cited is less than optimal. Does it make you a bad programmer that you did not recognize that? Probably not. It just means you never had someone goad you on asking if you can think of a better way. That is the reason these brain teasers are at best tangentially related to programming skill.

Anon:

vt_mruhlin:

I actually saw a good discussion of this one, and how that particular example can be used to guage programming skills. Correct solution was to do a binary sort on on. Put 4 coins on each side of the scale, discard the lighter half, weigh the remaining 4, then weigh the remaining two.....

I have to interview somebody for a position later this week and I was thinking of using that one (not so sure now).
You can actually do it quicker by splitting it into 3 groups. The 8 coin thing is deliberately misleading to make you think of splitting into 2 groups, but you should be able to do it with just two weighings if you split into three.
Still, I'd give bonus points for using the term "binary sort".

TimS:

Really, it's the approach that you're trying to see, not the answer. If someone shouts out the answer immediately, and recites the answer, as memorized, from a book of problems, that's an immediate check in the "no" column for me. On the other hand, if they have a good idea as to how the problem needs to be solved, that's a check in the "yes" column.

Grandpa:

Three players enter a room and a red or blue hat is placed on each person's head. The color of each hat is determined by a coin toss, with the outcome of one coin toss having no effect on the others. Each person can see the other players' hats but not his own.

No communication of any sort is allowed, except for an initial strategy session before the game begins. Once they have had a chance to look at the other hats, the players must simultaneously guess the color of their own hats or pass. The group shares a hypothetical $3 million prize if at least one player guesses correctly and no players guess incorrectly.

What strategy would you use?

Rodyland:

- You have a 3 litre jug and a 5 litre jug. How do you get exactly 4 litres into the 5 litre jug?
Fill the 3 litre jug, pour it into the 5 litre jug. Fill the 3 litre jug again, pour it into the 5 litre jug until the 5 litre jug is full. Now you have 5 litres in the 5 litre jug and one litre in the 3 litre jug. Empty the 5 litre jug (drink it if involves some type of alcoholic beverage). Now pour the remaining litre in the 3 litre jug into the 5 litre jug. Fill the 3 litre jug one more time and pour it into the 5 litre jug adding the 3 new litres to the one existing one. Voi la! Exactly 4 litres in a 5 litre jug.

- Why are manhole covers usually round?
Round is the only shape that guarantees, no matter how you orient the cover, that the cover will not fall into the manhole and onto the man in the hole. That's why I only ever use round covers on my manhole.

- You've got a chicken, a fox, and a bag of grain on one side of the river, and a boat that holds you and one of the chicken/fox/grain. If the fox is left alone with the chicken, he'll eat it. If the chicken is left alone with the grain, he'll eat it. How do you get all across the river so that nobody/nothing gets eaten.
Take chicken across, go back and get grain, take grain across, drop off grain and take chicken back, drop chicken off and take fox across, you now have fox and grain on destination side, go back and get chicken, take chicken across. Now everyone is safe on the destination side.
Now, send fox off to hunt rabbits, roast the chicken, make bread out of the grain, and eat a tastey dinner!

Hat problem - make the strategy be: The person who sees two other people with the same colour hat calls out the opposite colour. He's got a 3/4 chance in being right. There is a 1/4 chance that they are all the same colour, in which case they'll all call out the (wrong) opposite colour.