78 lines
2.5 KiB
Prolog
78 lines
2.5 KiB
Prolog
/* $Id$
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Part of CHR (Constraint Handling Rules)
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Author: Tom Schrijvers
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E-mail: Tom.Schrijvers@cs.kuleuven.be
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WWW: http://www.swi-prolog.org
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Copyright (C): 2003-2004, K.U. Leuven
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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as published by the Free Software Foundation; either version 2
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of the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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As a special exception, if you link this library with other files,
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compiled with a Free Software compiler, to produce an executable, this
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library does not by itself cause the resulting executable to be covered
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by the GNU General Public License. This exception does not however
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invalidate any other reasons why the executable file might be covered by
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the GNU General Public License.
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*/
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:- module(a_star,
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[
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a_star/4
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]).
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:- use_module(binomialheap).
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:- use_module(find).
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:- use_module(library(dialect/hprolog)).
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a_star(DataIn,FinalData,ExpandData,DataOut) :-
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a_star_node(DataIn,0,InitialNode),
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empty_q(NewQueue),
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insert_q(NewQueue,InitialNode,Queue),
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a_star_aux(Queue,FinalData,ExpandData,EndNode),
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a_star_node(DataOut,_,EndNode).
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a_star_aux(Queue,FinalData,ExpandData,EndNode) :-
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delete_min_q(Queue,Queue1,Node),
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( final_node(FinalData,Node) ->
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Node = EndNode
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;
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expand_node(ExpandData,Node,Nodes),
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insert_list_q(Nodes,Queue1,NQueue),
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a_star_aux(NQueue,FinalData,ExpandData,EndNode)
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).
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final_node(D^Call,Node) :-
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a_star_node(Data,_,Node),
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term_variables(Call,Vars),
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chr_delete(Vars,D,DVars),
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copy_term(D^Call-DVars,Data^NCall-DVars),
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call(NCall).
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expand_node(D^Ds^C^Call,Node,Nodes) :-
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a_star_node(Data,Score,Node),
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term_variables(Call,Vars),
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chr_delete(Vars,D,DVars0),
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chr_delete(DVars0,Ds,DVars1),
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chr_delete(DVars1,C,DVars),
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copy_term(D^Ds^C^Call-DVars,Data^EData^Cost^NCall-DVars),
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term_variables(Node,NVars,DVars),
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find_with_var_identity(ENode,NVars,(NCall,EScore is Cost + Score,a_star:a_star_node(EData,EScore,ENode)),Nodes).
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a_star_node(Data,Score,Data-Score).
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