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yap-6.3/packages/gecode/clp_examples/queens.yap

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2013-11-03 14:12:38 +00:00
:- use_module(library(gecode/clpfd)).
:- use_module(library(maplist)).
queens(N, Queens) :-
length(Queens, N),
Queens ins 1..N,
all_distinct(Queens),
foldl(inc, Queens, Inc, 0, _), % [0, 1, 2, .... ]
foldl(dec, Queens, Dec, 0, _), % [0, -1, -2, ... ]
all_distinct(Inc,Queens),
all_distinct(Dec,Queens),
labeling([], Queens).
inc(_, I0, I0, I) :-
I is I0+1.
dec(_, I0, I0, I) :-
I is I0-1.
lqueens(N, Queens) :-
length(Queens, N),
Queens ins 1..N,
all_distinct(Queens),
lconstrain( Queens, 0 ),
labeling([], Queens).
lconstrain([], _).
lconstrain( [Q|Queens], I0) :-
I is I0+1,
foldl(constrain(Q, I0), Queens, I, _),
lconstrain( Queens, I).
constrain(Q, I, R, J, J1) :-
J1 is J+1,
Q + I #\= R + J,
Q - I #\= R - J.