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February 2009

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

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").


If you have any problems you think we might enjoy, please send them in. All replies should be sent to: webmster@us.ibm.com