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--- sc330_f2016:smaplesolution.pl [2016/08/16 18:41]
dcostello created
+++ sc330_f2016:smaplesolution.pl [2021/06/30 23:42]
@@ Line 1: / Line 1: @@
-<code prolog>
-% Problem #1, "It's a tie", Dell Logic Puzzles, October 1999
-% Each man (mr so-and-so) got a tie from a relative.
-tie(cupids).
-tie(happy_faces).
-tie(leprechauns).
-tie(reindeer).
-mr(crow).
-mr(evans).
-mr(hurley).
-mr(speigler).
-relative(daughter).
-relative(father_in_law).
-relative(sister).
-relative(uncle).
-solve :-
-    tie(CrowTie), tie(EvansTie), tie(HurleyTie), tie(SpeiglerTie),
-    all_different([CrowTie, EvansTie, HurleyTie, SpeiglerTie]),
-    %This predicate first chooses some ties.
-    %It will choose the same tie for everybody, then repeatedly backtrack
-    %choosing different ties, until the all_different predicate is satisfied.
-    %It then does the same thing for relatives.
-    %There is a more efficent way of doing this, but this is the simplest.
-    relative(CrowRelative), relative(EvansRelative),
-    relative(HurleyRelative), relative(SpeiglerRelative),
-    all_different([CrowRelative, EvansRelative, HurleyRelative, SpeiglerRelative]),
-    %each list is a triple [mr, tie, relative]
-    %Notice we specify the mr, this is arbitrary we could have specified the tie
-    %as long as we cover all three dimentions
-    Triples = [ [crow, CrowTie, CrowRelative],
-                [evans, EvansTie, EvansRelative],
-                [hurley, HurleyTie, HurleyRelative],
-                [speigler, SpeiglerTie, SpeiglerRelative] ],
-    % 1. The tie with the grinning leprechauns wasn't a present from a daughter.
-    %The underscore, _, is a variable that could unify with anything, and you don't care what.
-    \+ member([_, leprechauns, daughter], Triples),
-%Negation isn't difficult, but it's tricky. Here's what you need to remember about negation:
-%Whether negation succeeds or fails, it cannot ever unify (instantiate) anything.
-%You can use negation to prevent certain unifications, as above, but you cannot use it to find out anything.
-    % 2. Mr. Crow's tie features neither the dancing reindeer nor the yellow happy faces.
-    \+ member([crow, reindeer, _], Triples),
-    \+ member([crow, happy_faces, _], Triples),
-    % 3. Mr. Speigler's tie wasn't a present from his uncle.
-    \+ member([speigler, _, uncle], Triples),
-    % 4. The tie with the yellow happy faces wasn't a gift from a sister.
-    \+ member([_, happy_faces, sister], Triples),
-    % 5. Mr Evans and Mr. Speigler own the tie with the grinning leprechauns
-    %    and the tie that was a present from a father-in-law, in some order.
-    ( (member([evans, leprechauns, _], Triples),
-       member([speigler, _, father_in_law], Triples)) ;
-      (member([speigler, leprechauns, _], Triples),
-       member([evans, _, father_in_law], Triples)) ),
-    % 6. Mr. Hurley received his flamboyant tie from his sister.
-    member([hurley, _, sister], Triples),
-    tell(crow, CrowTie, CrowRelative),
-    tell(evans, EvansTie, EvansRelative),
-    tell(hurley, HurleyTie, HurleyRelative),
-    tell(speigler, SpeiglerTie, SpeiglerRelative).
-% Succeeds if all elements of the argument list are bound and different.
-% Fails if any elements are unbound or equal to some other element.
-all_different([H | T]) :- member(H, T), !, fail.
-all_different([_ | T]) :- all_different(T).
-all_different([_]).
-tell(X, Y, Z) :-
-    write('Mr. '), write(X), write(' got the '), write(Y),
-    write(' tie from his '), write(Z), write('.'), nl.
-</code>

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