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yap-6.3/CLPBN/clpbn/topsort.yap
2008-10-22 00:44:02 +01:00

86 lines
2.4 KiB
Prolog

:- module(topsort, [topsort/2,
topsort/3,
reversed_topsort/2]).
:- use_module(library(rbtrees),
[rb_new/1,
rb_lookup/3,
rb_insert/4]).
:- use_module(library(lists),
[reverse/2]).
/* simple implementation of a topological sorting algorithm */
/* graph is as Node-[Parents] */
topsort(Graph0, Sorted) :-
rb_new(RB),
topsort(Graph0, [], RB, Sorted).
topsort(Graph0, Sorted0, Sorted) :-
rb_new(RB),
topsort(Graph0, Sorted0, RB, Sorted).
%
% Have children first in the list
%
reversed_topsort(Graph0, RSorted) :-
rb_new(RB),
topsort(Graph0, [], RB, Sorted),
reverse(Sorted, RSorted).
topsort([], Sort, _, Sort) :- !.
topsort(Graph0, Sort0, Found0, Sort) :-
add_nodes(Graph0, Found0, SortI, NewGraph, Found, Sort),
topsort(NewGraph, Sort0, Found, SortI).
add_nodes([], Found, Sort, [], Found, Sort).
add_nodes([N-Ns|Graph0], Found0, SortI, NewGraph, Found, NSort) :-
delete_nodes(Ns, Found0, NNs),
( NNs == [] ->
NewGraph = IGraph,
NSort = [N|Sort],
rb_insert(Found0, N, '$', FoundI)
;
NewGraph = [N-NNs|IGraph],
NSort = Sort,
FoundI = Found0
),
add_nodes(Graph0, FoundI, SortI, IGraph, Found, Sort).
delete_nodes([], _, []).
delete_nodes([N|Ns], Found, NNs) :-
rb_lookup(N,'$',Found), !,
delete_nodes(Ns, Found, NNs).
delete_nodes([N|Ns], Found, [N|NNs]) :-
delete_nodes(Ns, Found, NNs).
%
% add the first elements found by topsort to the end of the list, so we
% have: a-> [], b -> [], c->[a,b], d ->[b,c] gives [d,c,a,b|Sorted0]
%
reversed_topsort([], Sorted, Sorted) :- !.
reversed_topsort(Graph0, Sorted0, Sorted) :-
add_parentless(Graph0, [], SortedRest, New, Graph1, Sorted0),
delete_parents(Graph1, New, NoParents),
reversed_topsort(NoParents, SortedRest, Sorted).
add_parentless([], New, Sorted, New, [], Sorted).
add_parentless([Node-Parents|Graph0], New, Sorted, Included, Graph1, SortedRest) :-
% Parents = [], !,
ord_subtract(Parents,New,[]), !,
ord_insert(New, Node, NNew),
add_parentless(Graph0, NNew, Sorted, Included, Graph1, [Node|SortedRest]).
add_parentless([Node|Graph0], New, Sorted, Included, [Node|Graph1], SortedRest) :-
add_parentless(Graph0, New, Sorted, Included, Graph1, SortedRest).
delete_parents([], _, []).
delete_parents([Node-Parents|Graph1], Included, [Node-NewParents|NoParents]) :-
ord_subtract(Parents, Included, NewParents),
delete_parents(Graph1, Included, NoParents).