39 lines
743 B
Prolog
39 lines
743 B
Prolog
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:- use_module(library(gecode/clpfd)).
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:- use_module(library(maplist)).
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queens(N, Queens) :-
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length(Queens, N),
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Queens ins 1..N,
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all_distinct(Queens),
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foldl(inc, Queens, Inc, 0, _), % [0, 1, 2, .... ]
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foldl(dec, Queens, Dec, 0, _), % [0, -1, -2, ... ]
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all_distinct(Inc,Queens),
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all_distinct(Dec,Queens),
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labeling([], Queens).
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inc(_, I0, I0, I) :-
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I is I0+1.
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dec(_, I0, I0, I) :-
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I is I0-1.
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lqueens(N, Queens) :-
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length(Queens, N),
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Queens ins 1..N,
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all_distinct(Queens),
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lconstrain( Queens, 0 ),
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labeling([], Queens).
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lconstrain([], _).
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lconstrain( [Q|Queens], I0) :-
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I is I0+1,
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foldl(constrain(Q, I0), Queens, I, _),
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lconstrain( Queens, I).
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constrain(Q, I, R, J, J1) :-
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J1 is J+1,
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Q + I #\= R + J,
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Q - I #\= R - J.
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