[ghurtado]

I thought this was a great puzzle when I first saw it. IMHO, it is more satisfying to "think through it" without paper and pencil, since it is relatively simple to resolve.

The Python solution proposed is really great, in that it captures both the expressive and functional spirit of the language.

[ternaryoperator]

>since it is relatively simple to solve

You are overestimating how simple it is.There are more than 1200 comments on the solution on the NYTimes[1] almost all of them arguing that other dates are correct.

[1] http://www.nytimes.com/2015/04/15/science/answer-to-the-sing...

[baddox]

It's very simple in the context of logic puzzles. Similarly, the melody of "Ode to Joy" is very simple to play on the piano. That's not to say that there aren't at least 1,200 people unable to play it on the piano. But it is one of the simplest recognizable melodies to play on the piano, and is likely playable by the vast majority of people with a few months of piano lessons.

[chongli]

The hard part is not the logic, it's actually figuring out that this is a logic puzzle that needs to be solved by deduction and not a bunch of nonsense with terrible grammar. To borrow your Ode To Joy example, it's like trying to learn to play the piece after the sheet music had been torn and tattered, burned and stained with coffee. Sure, the music is simple once you get past all of the garbage in your way.

The original version of the puzzle (in the Singapore Math Olympiad) presented the dates in a sparse table format. This little bit of symbolic communication makes it much clearer that the answerer is supposed to cross off the dates by a process of deduction, making the puzzle simple to solve.

[baddox]

> The hard part is not the logic, it's actually figuring out that this is a logic puzzle that needs to be solved by deduction and not a bunch of nonsense with terrible grammar.

I am seeing this claim a lot, but I do not understand it. Why would readers assume that a riddle is a bunch of nonsense, rather than something with an objective answer?

> To borrow your Ode To Joy example, it's like trying to learn to play the piece after the sheet music had been torn and tattered, burned and stained with coffee.

I don't see the analogy, because I had no trouble understanding the wording of the puzzle. I thought it was extremely clear and precise. To use your analogy, I feel like I'm looking at a pristine professionally-notated piece of sheet music while everyone else is saying it's torn and tattered.

[chongli]

I am seeing this claim a lot, but I do not understand it. Why would readers assume that a riddle is a bunch of nonsense, rather than something with an objective answer?

Different people carry different assumptions with them throughout their lives. Not everybody approaches a logic puzzle with the mental preparation of solving logic puzzles. They aren't looking to analyze the statements and they don't carry the assumption that the statements carry just enough information to solve it. Instead, they might expect some trick or play on words to give a "stupid" answer.

because I had no trouble understanding the wording of the puzzle

But you do have trouble understanding that other people might be different from you; with different experiences, assumptions, etc.

[andrewprock]

"But you do have trouble understanding that other people might be different from you; with different experiences, assumptions, etc."

In essence, this is the true test of the puzzle; not whether you can solve the intended puzzle, but whether or not you can muster sufficient social and analytical empathy to work with others when your assumptions turn out to be incongruent with the intended assumptions.

[sukilot]

If you learned to play piano in a different notation, Western clef note sheet music would be cryptic. Not everyone has learned the same language of expressing precise concepts.

[baddox]

If someone is a non-native and less than fluent English speaker being presented with this problem in English, then I think your analogy holds. If they are fluent English speakers, however, then I think the inability to translate simple English statements into logical constraints is a failure to solve the logic puzzle itself, not a different type of failure indicating that the problem description is "cryptic" or confusing.

[sukilot]

Please don't confuse a different country's dialect of English with "terrible grammar"

[apricot]

Is "Yesterday I eat noodles" considered grammatically correct English in Singapore?

[x0054]

I have to admit, it took me more than 5 minutes to figure this one out, so if this was a test problem, I probably failed. Maybe I am not as smart as I think, but it's probably not as simple as people, including other comments to this post, make it out to be. The trick to the problem is pretty obvious right away, but what tripped me is improper perspective. Reading the comments on NY Times, I think this is the same thing that trips up most people as well.

After eliminating May and June because they have unique days, which is obvious, I got stuck trying to figure out how Albert would be able to figure out the date after knowing that Bernard now knows the date. So I got stuck on July 16, Aug. 15 and Aug. 17 for a while, because I could not figure out how Albert would know the date if he was told August as the month. It took me a few minutes (ok, like 5 or so, more then I care to admit to my self I suppose :) ) to figure out that my job wasn't to figure out how Albert new, but rather to figure out what the answer was IF Albert now knew the answer.

From that it's pretty easy, but it's the perspective that trips most people up.

[vacri]

It wouldn't have taken you so long if you had've just been doing logic in a classroom. This isn't a puzzle that was sprung on the students by surprise; it was part of their course.

[lifeisstillgood]

Trust me that is a very eloquent and perceptive explanation of your own failings, and how that applies to others experience. Whatever time limit was arbitrarily set for the "test" you pass the more important test with flying colours.

[InclinedPlane]

It is a simple logic problem, simpler than the vast majority of logic puzzles. The fact that an enormous number of people in the developed world have poor logical reasoning skills is an entirely separate issue.

[tiler]

There are some great examples among the comments of people vehemently defending their provably false beliefs.

[deciplex]

There are great examples of that in every comment thread ever.

[pbhjpbhj]

Fry (thinks): can't tell if being ironic or ...

[DannoHung]

This reminds me of the Blue/Brown eyed villager puzzle.

The trick is in figuring out what additional information is actually being added by whatever subsequent statements are being made.

It's weird. I usually have a lot of trouble with mathematical word puzzles. Particularly probability. But logic puzzles almost always seem to be pretty easy for me.

Now if you want a really fucking hard one, try your hand at this: http://en.wikipedia.org/wiki/The_Hardest_Logic_Puzzle_Ever

[Jach]

It's relatively simple, if you're the kind of person who grasps that 1+1*0 is not 0 under most parsers and under the order of operations implied by e.g. the vector space axioms...

[pdpi]

> under the order of operations implied by e.g. the vector space axioms

What, exactly, about vector spaces implies an order of operations?

[Jach]

See for reference: http://www.math.ucla.edu/~tao/resource/general/121.1.00s/vec... Addition is only defined on two elements of the space, multiplication is only defined for multiplying an element by a real number, which results in an element. These satisfy the unambiguous distributive axiom, real * (el_1 + el_2) = real * el_1 + real * el_2. Since addition only applies to elements, real * el_1 and real * el_2 must be computed into elements first before the sum. While this doesn't strictly, logically imply the same for real * real + real * real, it's at least suggestive (hence the e.g.) and you can turn to the Peano Arithmetic axioms and definitions of addition and multiplication and do the same thing for natural numbers. Or you can just say the ordering implied by assuming PEMDAS, but just saying that alone is boring and doesn't really expose the elegance in notation/algebraic transformation gained from such a convention.

(For those who don't get the reference, every so often some variant of "a + b * 0 + c = ?" will show up in the public's attention and receive very emotional arguments about how it must be 0, or must be a+c, or must be c, or it must be ambiguous and therefore undefined. Similarly to the logic puzzle programmers can just point to the problem expressed in Python for the correct answer...)

[sukilot]

But even in a vector space these examples are still ambiguous.

[cam_l]

This comment is, in itself, a description of the issue it raises. Simple is an ambiguous term, and you are using it to describe a different aspect of the problem to the parent (you are both right).

[nazri1]

Bike shedding, layman version.

[logicallee]

bike shedding[1] would be arguing over the names of albert, bernard, and cheryl - wouldn't Alice, Bob, and Carol be more conventional? Or something else that is easier to understand and argue about than the problem itself.

so, no, arguing about the actual problem isn't bikeshedding :)

[1] http://en.wikipedia.org/wiki/Parkinson%27s_law_of_triviality