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The New Coffee Room

  1. TNCR
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  3. Puzzle time - prisoners and hats

Puzzle time - prisoners and hats

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  • LuFins DadL LuFins Dad

    Are these male prisoners or female prisoners?

    8% of men are colorblind and .5% of women are.

    George KG Offline
    George KG Offline
    George K
    wrote on last edited by
    #21

    @lufins-dad said in Puzzle time - prisoners and hats:

    8% of men are colorblind and .5% of women are.

    Mens' eyes matter!

    "Now look here, you Baltic gas passer... " - Mik, 6/14/08

    The saying, "Lite is just one damn thing after another," is a gross understatement. The damn things overlap.

    1 Reply Last reply
    • jon-nycJ jon-nyc

      For the two color case - black and white:

      The last guy in line, who sees all hats except his own, calls out “black”, say, to communicate he can see an odd number of black hats. Otherwise, he says “white”, meaning he can see an even number of black hats.

      He of course has only a chance of guessing his own color.

      But the next guy will either see the same parity (odd/even) of black hats indicated in the first answer, or not. If he does, he can assume he has a white hat, if not he can assume black. Next in line same, after taking into account any ‘parity switch’ indicated by the second man’s stated color.

      By that method all but the last in line (first guy to call his color) are freed.

      Is there an analogous method for n colors?

      jon-nycJ Offline
      jon-nycJ Offline
      jon-nyc
      wrote on last edited by
      #22

      @jon-nyc said in Puzzle time - prisoners and hats:

      For the two color case - black and white:

      The last guy in line, who sees all hats except his own, calls out “black”, say, to communicate he can see an odd number of black hats. Otherwise, he says “white”, meaning he can see an even number of black hats.

      He of course has only a chance of guessing his own color.

      But the next guy will either see the same parity (odd/even) of black hats indicated in the first answer, or not. If he does, he can assume he has a white hat, if not he can assume black. Next in line same, after taking into account any ‘parity switch’ indicated by the second man’s stated color.

      By that method all but the last in line (first guy to call his color) are freed.

      Is there an analogous method for n colors?

      Big hint: I can use slightly different words to describe this very same method and it will scale to n colors.

      Only non-witches get due process.

      • Cotton Mather, Salem Massachusetts, 1692
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      • KlausK Offline
        KlausK Offline
        Klaus
        wrote on last edited by Klaus
        #23

        I guess the key operation is, as often in these kinds of puzzles, modulo n.

        So everyone announces sum of colors (colors are numbered one to n) mod # of colors...

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        • jon-nycJ Offline
          jon-nycJ Offline
          jon-nyc
          wrote on last edited by
          #24

          That’s exactly right.

          Only non-witches get due process.

          • Cotton Mather, Salem Massachusetts, 1692
          KlausK 1 Reply Last reply
          • jon-nycJ jon-nyc

            That’s exactly right.

            KlausK Offline
            KlausK Offline
            Klaus
            wrote on last edited by
            #25

            Or, more precisely, only the first to announce does this and everybody else announces his own color.

            1 Reply Last reply
            • HoraceH Offline
              HoraceH Offline
              Horace
              wrote on last edited by
              #26

              maga

              Education is extremely important.

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