"andrel" wrote:
> there are three of them, but indeed shooting them all seems to solve the 
> problem.

No, their function is not to stop you from entering the passages. They will 
let you through all right. The problem is that once you've entered a 
passage, there is no way back (for some reason) so you have to choose the 
right one the first time. The function of the guards is to give you 
information which you may use to figure out which passage to choose.

Oh, and if you're not familiar with the original riddle:

There are two passages of which you must choose one. One of them leads to 
freedom, the other one to doom. Once you have chosen one, you are stuck with 
it. In front of each passage is a guards. One guard always tell the truth 
and one always lies. You don't know which does what. Now you must find out 
which passage to choose by asking the guards questions...

Rune
-- 
http://runevision.com

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Rune wrote:
> 
> There are two passages of which you must choose one. One of them leads to 
> freedom, the other one to doom. Once you have chosen one, you are stuck with 
> it. In front of each passage is a guards. One guard always tell the truth 
> and one always lies. You don't know which does what. Now you must find out 
> which passage to choose by asking the guards questions...

Solving which one is which is actually easy. You just need to ask one of
them, if he lies precisely to half of the questions. If he speaks true,
he'll of course answer "no". If he always lies, he has to answer "yes".

> Rune


-- 
Eero "Aero" Ahonen
   http://www.zbxt.net
      aer### [at] removethiszbxtnetinvalid

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Invisible wrote:
> http://www.xkcd.com/246/

I saw a great solution where the wizard started explaining to everyone 
how the logic works and the warrior just shot one of them in the foot.

Left:  "Ow! You shot me in the foot!"
Right:  "No he didn't!"
Left: "I can't believe you just did that!"
Right: "Yes you can!"

-- 
   Darren New / San Diego, CA, USA (PST)
     It's not feature creep if you put it
     at the end and adjust the release date.

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Eero Ahonen wrote:
> Rune wrote:
>> There are two passages of which you must choose one. One of them leads to 
>> freedom, the other one to doom. Once you have chosen one, you are stuck with 
>> it. In front of each passage is a guards. One guard always tell the truth 
>> and one always lies. You don't know which does what. Now you must find out 
>> which passage to choose by asking the guards questions...
> 
> Solving which one is which is actually easy. 

The actual puzzle is that you only get to ask one question.

I've also seen it done with three creatures, one who tells the truth, 
one who lies, and one who picks at random. Except they don't speak your 
language: they speak a language where Jay and Dook mean yes and no, or 
maybe no and yes.

The solution is along the lines of "Would the second person answer Dook 
to the question of what the third person would answer if and only if the 
work Jay means "yes" in my language?"  Really convoluted, but it works out.

-- 
   Darren New / San Diego, CA, USA (PST)
     It's not feature creep if you put it
     at the end and adjust the release date.

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Rune <aut### [at] runevisioncom> wrote:
> There are two passages of which you must choose one. One of them leads to 
> freedom, the other one to doom. Once you have chosen one, you are stuck with 
> it. In front of each passage is a guards. One guard always tell the truth 
> and one always lies. You don't know which does what. Now you must find out 
> which passage to choose by asking the guards questions...

  The vast majority of people pose the problem like that, and they all get
it wrong. That's because that is not limiting the number of questions you
can ask, in which case the problem makes no sense as it becomes trivial.

  In the real problem you can only ask one question, period.

  (Curiously, that also means that having two guards is redundant. One
guard is enough.)

-- 
                                                          - Warp

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"Warp" wrote:
>  The vast majority of people pose the problem like that, and they all get
> it wrong. That's because that is not limiting the number of questions you
> can ask, in which case the problem makes no sense as it becomes trivial.
>
>  In the real problem you can only ask one question, period.

Yes I see that now.

>  (Curiously, that also means that having two guards is redundant. One
> guard is enough.)

Sure, but having two makes the question trickier for ones who are unfamiliar 
with the riddle, because it makes it seem like there are more factors 
involved.

Rune
-- 
http://runevision.com

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Rune <aut### [at] runevisioncom> wrote:
> >  (Curiously, that also means that having two guards is redundant. One
> > guard is enough.)

> Sure, but having two makes the question trickier for ones who are unfamiliar 
> with the riddle, because it makes it seem like there are more factors 
> involved.

  I wonder if it could work with more doors than two (ie. still having
one guard and one question, or if it's impossible, perhaps two questions).

-- 
                                                          - Warp

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Darren New wrote:
> Eero Ahonen wrote:
>> Rune wrote:
>>> There are two passages of which you must choose one. One of them 
>>> leads to freedom, the other one to doom. Once you have chosen one, 
>>> you are stuck with it. In front of each passage is a guards. One 
>>> guard always tell the truth and one always lies. You don't know which 
>>> does what. Now you must find out which passage to choose by asking 
>>> the guards questions...
>>
>> Solving which one is which is actually easy. 
> 
> The actual puzzle is that you only get to ask one question.
> 
> I've also seen it done with three creatures, one who tells the truth, 
> one who lies, and one who picks at random. Except they don't speak your 
> language: they speak a language where Jay and Dook mean yes and no, or 
> maybe no and yes.
> 
> The solution is along the lines of "Would the second person answer Dook 
> to the question of what the third person would answer if and only if the 
> work Jay means "yes" in my language?"  Really convoluted, but it works out.
> 
And in the puzzle stated in the top post, you'd have a change of 1/3 of 
being stabbed.

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> The solution is along the lines of "Would the second person answer Dook 
> to the question of what the third person would answer if and only if the 
> work Jay means "yes" in my language?"  Really convoluted, but it works out.
> 

My head asplode.

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On Wed, 16 Jan 2008 03:11:40 -0500, Warp wrote:

>   (Curiously, that also means that having two guards is redundant. One
> guard is enough.)

Not the way I've heard the question asked, which is:

"Which door would the other guard say is the safe door?"

Either way, the door indicated is not the safe door.

I guess with a single guard, you could ask the question:

"If you were to lie to me, which door would be the safe door?"

So I guess it would work after all. <g>

Jim

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