125 lines
3.3 KiB
Prolog
125 lines
3.3 KiB
Prolog
/* $Id$
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Part of SWI-Prolog
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Author: Jan Wielemaker
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E-mail: jan@science.uva.nl
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WWW: http://www.swi-prolog.org
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Copyright (C): 1985-2005, University of Amsterdam
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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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 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(nb_set,
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[ empty_nb_set/1, % -EmptySet
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add_nb_set/2, % +Key, !Set
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add_nb_set/3, % +Key, !Set, ?New
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gen_nb_set/2, % +Set, -Key
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size_nb_set/2, % +Set, -Size
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nb_set_to_list/2 % +Set, -List
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]).
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/** <module> Non-backtrackable sets
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This library provides a non-backtrackabe set. It is based on
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nb_setarg/3. See the SWI-Prolog manual for details.
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@author Jan Wielemaker
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@tbd Base this work on AVL trees rather then unbalanced trees.
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*/
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/*******************************
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* NON-BACKTRACKABLE SETS *
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*******************************/
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%% empty_nb_set(-Set)
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%
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% Create an empty non-backtrackable set.
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empty_nb_set(nb_set(t)).
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%% add_nb_set(+Key, !Set) is det.
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%% add_nb_set(+Key, !Set, ?New) is semidet.
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%
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% Insert an element into the set. If the element is already in the
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% set, nothing happens. New is =true= if Key was added as a new
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% element to the set and =false= otherwise.
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add_nb_set(Key, Set) :-
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add_nb_set(Key, Set, _).
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add_nb_set(Key, Set, New) :-
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( empty_nb_set(Set)
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-> New = true,
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nb_setarg(1, Set, t(Key, t, t))
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; arg(1, Set, Tree),
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'$btree_find_node'(Key, Tree, Node, Arg),
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( Arg == 1
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-> New = false
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; New = true,
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nb_setarg(Arg, Node, t(Key, t, t))
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)
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).
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%% nb_set_to_list(+Set, -List)
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%
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% Get the elements of a an nb_set. List is sorted to the standard
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% order of terms.
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nb_set_to_list(nb_set(Set), List) :-
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phrase(nb_set_to_list(Set), List).
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nb_set_to_list(t) -->
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[].
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nb_set_to_list(t(Val, Left, Right)) -->
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nb_set_to_list(Left),
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[Val],
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nb_set_to_list(Right).
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%% gen_nb_set(+Set, -Key)
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%
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% Enumerate the members of a set in the standard order of terms.
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gen_nb_set(nb_set(Tree), Key) :-
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gen_set(Tree, Key).
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gen_set(t(Val, Left, Right), Key) :-
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( gen_set(Left, Key)
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; Key = Val
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; gen_set(Right, Key)
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).
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%% size_nb_set(+Set, -Size)
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%
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% Unify Size with the number of elements in the set
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size_nb_set(nb_set(Tree), Size) :-
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set_size(Tree, Size).
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set_size(t, 0).
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set_size(t(_,L,R), Size) :-
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set_size(L, SL),
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set_size(R, SR),
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Size is SL+SR+1.
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