Couldn't resist. This is the solution ported to C#:
When Is Cheryl's Birthday?
41–50 of 136 posts
Re: When Is Cheryl's Birthday?
#42I 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.
>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...
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.
Re: When Is Cheryl's Birthday?
#43Here's my quick solution in modern SQL. This is more expensive than it needs to be, but doing it this way lets you see the truth table by commenting out the final predicate.
Re: When Is Cheryl's Birthday?
#44Maybe I'm missing something, but the "hard" part of this problem is figuring on the trick. Once you know that, it becomes relatively easy – and you can't use a program to figure out the trick.
Which part is the trick? It all seems very straightforward to me.
Its understanding what the question actually means when it says things like 'Bernard: At first I don't know when Cheryl's birthday is, but I know now.' ... this is actually a cryptic coding of the rules of the puzzle.
If you properly understand those rules and convert them to code (as in the OP) then searching the possible answers for a match is trivial.
Re: When Is Cheryl's Birthday?
#45Maybe I'm missing something, but the "hard" part of this problem is figuring on the trick. Once you know that, it becomes relatively easy – and you can't use a program to figure out the trick.
Which part is the trick? It all seems very straightforward to me.
The trick is to take it at face value and not question how they know, but what the answer has to be assuming they do know.
Re: When Is Cheryl's Birthday?
#46Earlier quoted context omitted.
Which part is the trick? It all seems very straightforward to me.
Its understanding what the question actually means when it says things like 'Bernard: At first I don't know when Cheryl's birthday is, but I know now.' ... this is actually a cryptic coding of the rules of the puzzle. If you properly understand those rules and convert them to code (as in the OP) then searching the possible answers for a match is trivial.
Why do you say that is cryptic? I can't think of a clearer or plainer way to express that fact.
Re: When Is Cheryl's Birthday?
#47Earlier quoted context omitted.
Which part is the trick? It all seems very straightforward to me.
The trick is to take it at face value and not question how they know, but what the answer has to be assuming they do know.
Assuming that the problem is posed and understood as an artificial puzzle (rather than a real scenario with real people), what reason would there be to question how they know? Of course you're supposed to assume they know. It's a puzzle, and someone is telling you precisely what you're to assume.
Re: When Is Cheryl's Birthday?
#48Earlier quoted context omitted.
>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...
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 th…
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.
Re: When Is Cheryl's Birthday?
#49Earlier quoted context omitted.
Its understanding what the question actually means when it says things like 'Bernard: At first I don't know when Cheryl's birthday is, but I know now.' ... this is actually a cryptic coding of the rules of the puzzle. If you properly understand those rules and convert them to code (as in the OP) then searching the possible answers for a match is trivial.
Why do you say that is cryptic? I can't think of a clearer or plainer way to express that fact.
Trust me, its cryptic to most people, and that's why this puzzle has gone viral round the world in an omg-singapore-schoolkids-can-do-this-insane-puzzle kind of way.
Re: When Is Cheryl's Birthday?
#50Earlier quoted context omitted.
These are actually valid questions and you shouldn't be downvoted. The standard interpretation of the problem is highly questionable; Albert's initial remark is not actually dispositive to Bernhard, because if Bernhard had the 19 May date he would know the correct answer immediately without needing Albert to say anything. The suggestion that Albert's first statement necessarily eliminates all dates in May is false, a…
can you make your whole comment more explicit, I don't follow your objection.
Let's consider the question:
1. "Why did Albert speak first?"
Before we answer this, we need to develop a set of assumptions to operate under. Given the synthetic nature of the problem, we might assume that both Albert and Bernard are of equal ability, and able to make logical inferences based on reasonable assumptions. We'll also assume that both Albert and Bernard are only going to announce the binary state of each others certainty of the answer. Lastly, we'll assume that whoever can deduce the binary state of certainty first, will speak first.
These assumptions, while a bit presumptuous, seem on the surface to adhere to the spirit of the puzzle.
Given those assumptions, what does it mean when Albert speaks first? It means that he's figured out the binary state of certainty before Bernard. How could that be?
If Bernard has the dates 18 or 19, then he knows that he knows, and he also knows that Albert does not know. If Bernard has any other date, he'll know that they both don't know. How does Bernard make this determination? He checks if his date is repeated anywhere.
Compare that to the logic that Albert must perform to rule out Bernard's certainty. He must check that all of the dates in his month are in fact repeated.
If they both perform these mental operations at the same speed, then Bernard should speak first in the case where he knows a unique date. The only reason why Bernard might not speak first is that he must also reason through whether or not Albert might know the date at this point. If Bernard holds an unrepeated date, the complexity of reasoning through Alberts situation boils down to considering only one month. But if Bernard holds a repeated date, he must consider Albert's situation for two months.
So, there exists a time past which Albert must know that Bernard is considering the more difficult situation, and thus he can infer that Bernard does not know.
If one assumes precise knowledge of the timing of logical operations, one can make even stronger inferences. To the point of even solving the entire problem without anyone every saying anything, for specific birthdays.
I will be the first to admit that this line of reasoning may require certain assumptions which are strained. Thus the question may still remain:
1. "Why did Albert speak first?"
Does anyone have a different set of logical assumptions which leads to Albert speaking first?
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What this exposes really, is the more subtle assumption that the "correct" solution makes:
"There is only one way to make inferences in this puzzle."
The truth of that statement depends very much on the assumptions one makes about the puzzle. Most problematic is that most assumptions which makes that true, make it impossible for Albert to be the first speaker.
It's a kind of logical paradox brought on by the fact that synthetic logic problems do not map very well to real world situations.