f5e660b9a3
git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1114 b08c6af1-5177-4d33-ba66-4b1c6b8b522a
106 lines
1.8 KiB
Plaintext
106 lines
1.8 KiB
Plaintext
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:- object(eight_puzzle,
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instantiates(heuristic_state_space)).
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:- info([
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version is 1.1,
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author is 'Paulo Moura',
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date is 2004/8/15,
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comment is 'Eight puzzle heuristic state space search problem.']).
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:- uses(list, [member/2]).
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initial_state(four_steps, [2/2,1/3,3/2,2/3,3/3,3/1,2/1,1/1,1/2]).
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initial_state(five_steps, [2/1,1/2,1/3,3/3,3/2,3/1,2/2,1/1,2/3]).
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initial_state(eighteen_steps, [2/2,2/3,1/3,3/1,1/2,2/1,3/3,1/1,3/2]).
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goal_state(goal, [2/2,1/3,2/3,3/3,3/2,3/1,2/1,1/1,1/2]).
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print_state([S0,S1,S2,S3,S4,S5,S6,S7,S8]) :-
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member(Y, [3, 2, 1]),
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nl,
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member(X, [1, 2, 3]),
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member(Tile-X/Y, [' '-S0,1-S1,2-S2,3-S3,4-S4,5-S5,6-S6,7-S7,8-S8]),
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write(Tile),
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fail.
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print_state(_) :-
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nl.
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next_state([Empty| L], [Tile| L2], 1) :-
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swap(Empty, Tile, L, L2).
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swap(Empty, Tile, [Tile| L], [Empty| L]) :-
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dist(Empty, Tile, 1).
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swap(Empty, Tile, [Tile2| L], [Tile2| L2]) :-
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swap(Empty, Tile, L, L2).
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dist(X/Y, X2/Y2, D) :-
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abs_diff(X, X2, Dx),
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abs_diff(Y, Y2, Dy),
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D is Dx + Dy.
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abs_diff(A, B, D) :-
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A > B ->
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D is A - B
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;
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D is B - A.
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heuristic([_| L], H) :-
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goal_state(_, [_| G]),
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totdist(L, G, 0, D),
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seq(L, S),
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H is D + 3*S.
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totdist([], [], D, D).
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totdist([T| L], [T2| L2], Acc, D) :-
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dist(T, T2, D1),
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Acc2 is Acc + D1,
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totdist(L, L2, Acc2, D).
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seq([First| L], S) :-
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seq([First| L], First, 0, S).
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seq([T1, T2| L], First, Acc, S) :-
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score(T1, T2, S1),
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Acc2 is Acc + S1,
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seq([T2| L], First, Acc2, S).
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seq([Last], First, Acc, S) :-
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score(Last, First, Score),
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S is Acc + Score.
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score(2/2, _, 1) :- !.
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score(1/3, 2/3, 0) :- !.
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score(2/3, 3/3, 0) :- !.
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score(3/3, 3/2, 0) :- !.
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score(3/2, 3/1, 0) :- !.
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score(3/1, 2/1, 0) :- !.
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score(2/1, 1/1, 0) :- !.
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score(1/1, 1/2, 0) :- !.
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score(1/2, 1/3, 0) :- !.
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score(_, _, 2) :- !.
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:- end_object.
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