Puzzle
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Ponder This Challenge - February 2009 - Find a bug in this unknown riddle

Ponder This Challenge:

Note: Because February's challenge was very difficult, we postponed the submission deadline by a month and we'll post the solution on April 1st.

The following list of numbers is a solution to a riddle. What is the riddle? What is the single error in it?

Hint (02/11): Look at the table as a bitmap

Hint (02/16): http://www.99main.com/~charlief/brl/brl2.htm

Hint (02/24): The riddle is a slight variation on one of the riddles from http://www.tanyakhovanova.com/Puzzles.

Hint (03/03): If (radioactive) then ... else ...

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Solution

  • When translating the hexadecimal numbers into a bitmap we get the first clue: "BRAILLE^".

    Following the arrow in the same bitmap, we see the second clue written in Braille code:

    "msb 0:found 1:question 2 out of 15 in 7 questions"

    The list of numbers is a solution to the riddle of finding a subset of size 2 out of 15, by asking 7 questions. Each question asks whether the 2 unknowns intersect a specific subset.

    The solution is coded as a binary tree, where after each question we recursively code the subtree for empty intersection and then code the subtree for non-empty intersection.

    In some cases, our riddle could have been solved in less than 7 questions and we added some dummy questions to make room for the clues.

    The single error is in the 19th word, which should be 6000 instead of 3e00 (it is part of the first "L" in "BRAILLE").

Solvers

  • Eugene Vasilchenko (02/02/2009 07:45 PM EDT)
  • Peter Mattsson (03/01/2009 05:19 PM EDT)
  • Tim Lewis (03/06/2009 11:57 AM EDT)
  • Gary M Gerken (03/15/2009 02:19 AM EDT)
  • Daniel Bitin (03/15/2009 01:02 PM EDT)
  • Tom Sirgedas (03/18/2009 07:11 PM EDT)
  • Kai Guttmann (03/30/2009 09:32 PM EDT)
  • Kin Keung Ma (Partial solution)

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