59 lines
1.4 KiB
Plaintext
59 lines
1.4 KiB
Plaintext
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:- object(breadth_first(Bound),
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instantiates(blind_search(Bound))).
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:- info([
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version is 1.0,
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authors is 'Paulo Moura',
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date is 1998/3/23,
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comment is 'Breadth first state space search strategy.',
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parnames is ['Bound']]).
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:- uses(list).
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search(Space, State, Bound, Solution) :-
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breadt(Space, l(State), Bound, Path),
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list::reverse(Path, Solution).
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breadt(Space, Tree, Bound, Solution) :-
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expand([], Tree, Tree2, Solved, Solution, Space, Bound),
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(Solved ->
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true
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;
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breadt(Space, Tree2, Bound, Solution)).
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expand(Path, l(State), _, true, [State| Path], Space, _) :-
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Space::goal_state(State).
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expand(Path, l(State), t(State, Subs), fail, _, Space, Bound) :-
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Bound > 0,
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bagof(l(Next),
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(Space::next_state(State, Next),
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\+ list::member(Next, [State| Path])),
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Subs).
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expand(Path, t(State,Subs), t(State, Subs2), Solved, Solution, Space, Bound) :-
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expandall([State| Path], Subs, [], Subs2, Solved, Solution, Space, Bound).
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expandall(_, [], [Tree| Trees], [Tree| Trees], fail, _, _, _).
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expandall(Path, [Tree| Trees], Trees2, Subs2, Solved, Solution, Space, Bound) :-
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Bound > 0,
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Bound2 is Bound -1,
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expand(Path, Tree, Tree2, Solved2, Solution, Space, Bound2),
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(Solved2 ->
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Solved = true
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;
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expandall(Path, Trees, [Tree2| Trees2], Subs2, Solved, Solution, Space, Bound))
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;
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expandall(Path, Trees, Trees2, Subs2, Solved, Solution, Space, Bound).
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:- end_object.
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