783ae4b9a0
improve redblack trees and use it to reimplement association lists and to have better implementation of several graph algorithms. git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1591 b08c6af1-5177-4d33-ba66-4b1c6b8b522a
87 lines
2.4 KiB
Prolog
87 lines
2.4 KiB
Prolog
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:- module(topsort, [topsort/2,
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topsort/3,
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reversed_topsort/2]).
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:- use_module(library(rbtrees),
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[rb_new/1,
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rb_lookup/3,
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rb_insert/4]).
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:- use_module(library(lists),
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[reverse/2]).
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/* simple implementation of a topological sorting algorithm */
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/* graph is as Node-[Parents] */
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topsort(Graph0, Sorted) :-
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rb_new(RB),
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topsort(Graph0, [], RB, Sorted).
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topsort(Graph0, Sorted0, Sorted) :-
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rb_new(RB),
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topsort(Graph0, Sorted0, RB, Sorted).
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%
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% Have children first in the list
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%
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reversed_topsort(Graph0, RSorted) :-
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rb_new(RB),
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topsort(Graph0, [], RB, Sorted),
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reverse(Sorted, RSorted).
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topsort([], Sort, _, Sort) :- !.
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topsort(Graph0, Sort0, Found0, Sort) :-
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add_nodes(Graph0, Found0, SortI, NewGraph, Found, Sort),
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topsort(NewGraph, Sort0, Found, SortI).
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add_nodes([], Found, Sort, [], Found, Sort).
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add_nodes([N-Ns|Graph0], Found0, SortI, NewGraph, Found, NSort) :-
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(N=1600 -> write(Ns), nl ; true),
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delete_nodes(Ns, Found0, NNs),
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( NNs == [] ->
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NewGraph = IGraph,
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NSort = [N|Sort],
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rb_insert(Found0, N, '$', FoundI)
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;
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NewGraph = [N-NNs|IGraph],
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NSort = Sort,
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FoundI = Found0
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),
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add_nodes(Graph0, FoundI, SortI, IGraph, Found, Sort).
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delete_nodes([], _, []).
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delete_nodes([N|Ns], Found, NNs) :-
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rb_lookup(N,'$',Found), !,
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delete_nodes(Ns, Found, NNs).
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delete_nodes([N|Ns], Found, [N|NNs]) :-
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delete_nodes(Ns, Found, NNs).
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%
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% add the first elements found by topsort to the end of the list, so we
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% have: a-> [], b -> [], c->[a,b], d ->[b,c] gives [d,c,a,b|Sorted0]
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%
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reversed_topsort([], Sorted, Sorted) :- !.
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reversed_topsort(Graph0, Sorted0, Sorted) :-
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add_parentless(Graph0, [], SortedRest, New, Graph1, Sorted0),
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delete_parents(Graph1, New, NoParents),
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reversed_topsort(NoParents, SortedRest, Sorted).
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add_parentless([], New, Sorted, New, [], Sorted).
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add_parentless([Node-Parents|Graph0], New, Sorted, Included, Graph1, SortedRest) :-
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% Parents = [], !,
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ord_subtract(Parents,New,[]), !,
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ord_insert(New, Node, NNew),
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add_parentless(Graph0, NNew, Sorted, Included, Graph1, [Node|SortedRest]).
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add_parentless([Node|Graph0], New, Sorted, Included, [Node|Graph1], SortedRest) :-
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add_parentless(Graph0, New, Sorted, Included, Graph1, SortedRest).
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delete_parents([], _, []).
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delete_parents([Node-Parents|Graph1], Included, [Node-NewParents|NoParents]) :-
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ord_subtract(Parents, Included, NewParents),
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delete_parents(Graph1, Included, NoParents).
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