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Solving a logic puzzle using Prolog

Asked 2009-12-21T09:16:49.470
11

The criminal is one of A, B, C and D.

A says: "It's not me"
B says: "It's D"
C says: "It's B"
D says: "It's not me"

And we know that only one of them tells the truth.

Who is the one? I want to solve it by using Prolog.

It's an interview question.

prolog puzzle
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1 Answer

3

I ran across this problem and wanted to give it a shot :

a(K) :- K \== a.
b(d).
c(b).
d(K) :- K \== d.

solve(TruthTeller) :-
    member(K, [a, b, c, d]),
    xor([a(K), b(K), c(K), d(K)], Truth),
    Truth =.. [TruthTeller|_].

xor([Head|Tail], Result) :-
    (   call(Head)
     -> forall(member(X, Tail), \+ call(X)), Result = Head
     ;  xor(Tail, Result)).
answered 2011-12-18T20:29:36.367

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