Riddle Thread

This is a discussion on Riddle Thread within the A Brief History of Cprogramming.com forums, part of the Community Boards category; Hey that's pretty cool, though. Nice one....

  1. #31
    Guest Sebastiani's Avatar
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    Hey that's pretty cool, though. Nice one.
    Code:
    if( numeric_limits< byte >::digits != bits_per_byte )
        error( "program requires bits_per_byte-bit bytes" );
    24bbs.cpp

  2. #32
    Cat without Hat CornedBee's Avatar
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    Riddle #3: three dwarfs, two paths, one life

    Giant In the Playground Games

    That's all I'll say.
    Last edited by CornedBee; 03-28-2009 at 11:42 AM.
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  3. #33
    Crazy Fool Perspective's Avatar
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    Riddle #3: three dwarfs, two paths, one life

    There's a whole book of these problem called Knights and Knaves, something like this:
    Knights and Knaves: Knights and Knaves Logic Puzzle

    Knights always tell the truth and Knaves always lie. There was a second book about Humans and Vampires. Humans always tell the truth, vampires always lie, insane humans think they are telling the truth but lie, and insane vampires think they are lying but always tell the truth. Then there's a bunch of riddles of this sort.

    If you like this, also check out The Puzzling Adventures of Dr. Ecco
    Last edited by CornedBee; 03-28-2009 at 11:42 AM.

  4. #34
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    Number theory in 21 minutes

    Its faster to just check if a number, modulo 6469693230 has a prime remainder, since all prime numbers do.
    Last edited by CornedBee; 03-28-2009 at 11:42 AM.
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  5. #35
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    Number theory in 21 minutes

    The greatest common factor explanation of this is great
    Last edited by CornedBee; 03-28-2009 at 11:43 AM.

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  6. #36
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    Number theory in 21 minutes

    >> Its faster to just check if a number, modulo 6469693230 has a prime remainder, since all prime numbers do.

    Are you sure about that? Can you elaborate?
    Last edited by CornedBee; 03-28-2009 at 11:43 AM.
    Code:
    if( numeric_limits< byte >::digits != bits_per_byte )
        error( "program requires bits_per_byte-bit bytes" );
    24bbs.cpp

  7. #37
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    Riddle #3: three dwarfs, two paths, one life

    Ok, just to bring this to an end:

    First, you ask a random dwarf: "Who of your brothers lies more often?"

    If you happen to ask A, he will correctly point to C.
    If you happen to ask B, he will incorrectly point to C.
    If you happen to ask C, he will randomly point to either A or B.

    In either case, the dwarf not asked and not pointed to is not C.

    Ask this dwarf the following question: "Which path would the dwarf suggest who is the exact opposite of you?"

    If you ask A, he will tell the truth and provide you with the path that B would've suggested, i.e. the wrong path.
    If you ask B, he will lie and provide you with the path that A would'nt have suggested, i.e. the wrong path.

    So you take the other path.

    Greets,
    Philip
    Last edited by CornedBee; 03-28-2009 at 11:43 AM.
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  8. #38
    C++ Witch laserlight's Avatar
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    Riddle #3: three dwarfs, two paths, one life

    hmm... but that seems to assume that the dwarves are benevolent. If they are (or more accurately, could be) malicious, then you have to phrase that second question more explicitly to your advantage.
    Last edited by CornedBee; 03-28-2009 at 11:44 AM.
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  9. #39
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    Riddle #5: more dwarfs

    There are seven dwarfs, each one wearing a unique hat. A wind blows off the hats. The dwarfs start running after their hats and each dwarf puts on the first hat that he manages to catch. Eventually every dwarf has a hat again.

    What is the probability that exactly six dwarfs are wearing their own hat now?

    Greets,
    Philip
    All things begin as source code.
    Source code begins with an empty file.
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  10. #40
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    Riddle #3: three dwarfs, two paths, one life

    Quote Originally Posted by laserlight View Post
    hmm... but that seems to assume that the dwarves are benevolent. If they are (or more accurately, could be) malicious, then you have to phrase that second question more explicitly to your advantage.
    Right. I already had several discussions about that. The problem arises due to the inexactness of most natural languages. The most obvious solution is to ask a more concise (and more awful) question. Personally, I prefer adding the proposition to the riddle that the dwarfs are benevolent. I didn't do it in the first place because it only distracts from the intended solution, but it's good that you pointed it out.

    Greets,
    Philip
    Last edited by CornedBee; 03-28-2009 at 11:44 AM.
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  11. #41
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    Riddle #3: three dwarfs, two paths, one life

    Quote Originally Posted by Snafuist
    The problem arises due to the inexactness of most natural languages.
    I don't think so. I think that it is merely an unstated assumption. I wanted to propose the solution of just capturing the dwarves and dragging them in a direction to see their response, but then I realised that I could not be sure that the dwarves were not so bored with their existence that they intended suicide, hence I would have to ask them questions anyway
    Last edited by CornedBee; 03-28-2009 at 11:44 AM.
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  12. #42
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    Riddle #4: if-statement considered harmful

    Oops, I skipped #4, so here it is.

    Consider the following program:

    Code:
    int cmp(int a, int b)
    {
            if(a > b) {
                    return 1;
            } else if(a < b) {
                    return -1;
            } else {
                    return 0;
            }
    }
    Can you come up with an implementation that doesn't use conditionals, i.e. if, for, while, switch?

    Greets,
    Philip
    All things begin as source code.
    Source code begins with an empty file.
    -- Tao Te Chip

  13. #43
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    Riddle #4: if-statement considered harmful

    I presume that includes ternary operator, and that this is either C or C++?
    Last edited by CornedBee; 03-28-2009 at 11:45 AM.
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  14. #44
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    Riddle #4: if-statement considered harmful

    Code:
    return (a >b)?1:(a<b)?-1:0;
    --
    Mats
    Last edited by CornedBee; 03-28-2009 at 11:45 AM.
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  15. #45
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    Riddle #5: more dwarfs

    I would say that equals (6!/(6*5!))-1.
    Last edited by CornedBee; 03-28-2009 at 11:45 AM.

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