[net.puzzle] Solution to liar/truth-teller/diplomat problem

anderson@uwvax.ARPA (David P. Anderson) (09/05/84)

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I have decided to *disallow* the solution posted by Eileen Rieback
because it involves questions which are yes/no/maybe rather than yes/no.
Eileen forfeits the $1000.00 first prize as a result.

Recall:
	truth-teller correctly answers all yes/no questions
	liar incorrectly answers all yes/no questions
	diplomat answers yes/no randomly
Your task: given one each of the above, ask 3 yes/no questions to
	figure out which is which.

SOLUTION: (call them X, Y and Z)

Ask X "Is your being a truth-teller equivalent to Y being a diplomat?"
If the answer is "yes"
    either X or Y is the diplomat
    Ask Z "Is your being a truth-teller equivalent to Y being a diplomat?"
    If the answer is "yes"
        Y is the diplomat
    else
        X is the diplomat
else
    either X or Z is the diplomat
    Ask Y "Is your being a truth-teller equivalent to X being a diplomat?"
    If the answer is "yes"
        X is the diplomat
    else
        Z is the diplomat

Now that you know who the diplomat is, you can distinguish the other two
by asking either of them a trivially true question such as "do you know
who the diplomat is?".

David Anderson (uwvax!anderson)

esr@iheds.UUCP (E. Rieback) (09/12/84)

> I have decided to *disallow* the solution posted by Eileen Rieback
> because it involves questions which are yes/no/maybe rather than yes/no.
> Eileen forfeits the $1000.00 first prize as a result.

What a shame!  I was hoping to spend the money on a lifetime
subscription to Games Magazine....

And as to your solution, I'm a little perplexed.  If X is indeed the
diplomat, the answer to the first question would be completely
random.  So how can you determine by X's answer who can be ruled out
as diplomat???

Eileen *disallowed* Rieback
ihnp4!iheds!esr