Solving a logic puzzle using Prolog

Question

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\"

Answer 1

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)).