2001-06-06 21:07:01 +01:00
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:- object(permute,
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extends(salesman)).
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:- info([
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2003-02-05 00:15:28 +00:00
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author is 'Paulo Moura',
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2001-06-06 21:07:01 +01:00
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version is 1.0,
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date is 2000/4/22,
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comment is '.',
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source is 'Example adopted from the Francis G. McCabe L&O documentation.']).
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:- op(400, yfx, ~).
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route(Towns, Route) :-
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findall(
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(Towns2, Length),
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(permute(Towns, Towns2), route_length(Towns2, Length)),
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List),
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shortest(List, Route).
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permute([Town], Town).
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permute(Towns, Towns2~Town) :-
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delete(Towns, Town, Towns3),
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permute(Towns3, Towns2).
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delete([Head| Tail], Head, Tail).
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delete([Head| Tail], Element, [Head| Tail2]):-
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delete(Tail, Element, Tail2).
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route_length(Town, 0) :-
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atom(Town), !.
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route_length(Towns~Town1~Town2, Length) :-
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!,
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route_length(Towns~Town1, Length1),
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Town1::crow_flies(Town2, Length2),
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Length is Length1 + Length2.
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route_length(Town1~Town2, Length) :-
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Town1::crow_flies(Town2, Length).
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shortest(List, Shortest) :-
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shortest(List, null, 1000000, Shortest).
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shortest([], Route, Length, (Route, Length)).
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shortest([(Route, Length)| Routes], _, LX, Shortest) :-
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Length < LX, !,
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shortest(Routes, Route, Length, Shortest).
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shortest([_| Routes], RX, LX, Shortest) :-
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shortest(Routes, RX, LX, Shortest).
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:- end_object.
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