/*
The description of this puzzle is easily found on the web. For example:
http://www.csci.csusb.edu/dick/cs320/prolog/Potions.htm
*/
:- object(potions).
:- info([
version is 1.2,
date is 2006/3/26,
author is 'Paulo Moura',
comment is 'Harry Potter potions logical puzzle.']).
:- uses(list, [select/3]).
:- public(potions/7).
:- mode(potions(?atom, ?atom, ?atom, ?atom, ?atom, ?atom, ?atom), zero_or_one).
:- info(potions/7, [
comment is 'Contents of the seven potions.',
argnames is ['P1', 'P2', 'P3', 'P4', 'P5', 'P6', 'P7']]).
contents([wine, wine, poison, poison, poison, forward, backwards]).
potions(P1, P2, P3, P4, P5, P6, P7) :-
contents(H1),
select(P1, H1, H2),
select(P7, H2, H3),
P1 \== P7, P1 \== forward, P7 \== forward, % second clue
select(P2, H3, H4),
P2 \== poison,
select(P3, H4, H5),
P3 \== poison, % third clue
select(P6, H5, H6), % fourth clue
P2 == P6,
select(P4, H6, H7),
select(P5, H7, []),
two_pairs_poison_wine([P1, P2, P3, P4, P5, P6, P7]). % first clue
two_pairs_poison_wine(S) :-
poison_wine_pair(S, R),
poison_wine_pair(R, _).
poison_wine_pair([poison, wine| R], R) :-
!.
poison_wine_pair([_| L], R) :-
poison_wine_pair(L, R).
:- end_object.
