92 lines
1.7 KiB
Plaintext
92 lines
1.7 KiB
Plaintext
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:- object(incremental,
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extends(salesman)).
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:- info([
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authors is 'Paulo Moura',
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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([Town| Towns], Route) :-
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route(Towns, Town, Route).
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route([], Route, Route).
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route([Town| Towns], Route, Route2) :-
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best_place(Route, Town, Best),
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split(Best, Route, Town, NewR),
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route(Towns, NewR, Route2).
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best_place(Route~Town1, Town, Best) :- % try the back first ...
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atom(Town1),
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Town::crow_flies(Town1, Distance),
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best_place(Route~Town1, Town, Distance, 0, 0, Best).
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best_place(Town, _, 0) :-
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atom(Town).
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best_place(R~T1~T2, T, XD, _, I, Best) :-
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atom(T1),
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atom(T2),
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extra(T1, T, T2, XT),
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XT < XD,
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I2 is I + 1,
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best_place(R~T1, T, XT, I2, I2, Best).
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best_place(R~T1~T2, T, XD, XI, I, Best) :-
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atom(T1),
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atom(T2),
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I2 is I + 1,
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best_place(R~T1, T, XD, XI, I2, Best).
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best_place(T1~T2, T, XD, _, I, Best) :-
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atom(T1),
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atom(T2),
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extra(T1, T, T2, XT),
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XT < XD,
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I2 is I + 1,
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best_place(T1, T, XT, I2, I2, Best).
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best_place(T1~T2, T, XD, XI, I, Best) :-
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atom(T1),
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atom(T2),
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I2 is I + 1,
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best_place(T1, T, XD, XI, I2, Best).
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best_place(T1, T, XD, _, I, Best) :-
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atom(T1),
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T1::crow_flies(T, Distance),
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Distance < XD,
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Best is I + 1.
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best_place(_, _, _, XI, _, XI).
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split(0, Route, Town, Route~Town).
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split(IX, Route~Town1, Town, S~Town1) :-
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IX2 is IX -1,
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split(IX2, Route, Town, S).
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split(1, Route, Town, Town~Route).
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extra(T1, T, T2, XT) :-
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T1::crow_flies(T, Distance1),
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T::crow_flies(T2, Distance2),
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T1::crow_flies(T2, Distance3),
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XT is Distance1 + Distance2 - Distance3.
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:- end_object.
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