x**o
发帖数: 1 | 1 This interesting problem was in the Moscow Math Olympiad
in spring 2000.
The deck of cards contains seven cards labeled
0,1,2,3,4,5,6. The cards are shuffled and distributed
among three people A,B,C. A and B receive three cards
each; the remaining card is given to C.
Question: assume each of A and B can speak one number,
can A and B exchange information about their
cards (ensuring that B knows A's cards and vice versa),
speaking in presence of C, in such a way that C still
cannot name any card ( | a******t
发帖数: 100 | 2 If you know something about cryptology, it is not difficult.
One method could be the following, though I have not proved it.
Suppose A has x, y, z. A just says (x + y + z) mod 7.
B does the same calculation and speak out the result.
The sum of all numbers are 0. A and B can know
which card C holds, thus know what cards B and A hold.
C can not guess three numbers by only knowing the numbers A and B say.
Actually, C can predict what B will say after knowing A's number. But he
can not know what thr
【在 x**o 的大作中提到】
: This interesting problem was in the Moscow Math Olympiad
: in spring 2000.
: The deck of cards contains seven cards labeled
: 0,1,2,3,4,5,6. The cards are shuffled and distributed
: among three people A,B,C. A and B receive three cards
: each; the remaining card is given to C.
: Question: assume each of A and B can speak one number,
: can A and B exchange information about their
: cards (ensuring that B knows A's cards and vice versa),
: speaking in presence of C, in such a way that C still
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