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yap-6.3/packages/gecode/examples/queens.yap
2013-11-03 14:12:38 +00:00

67 lines
2.1 KiB
Prolog

%% -*- prolog -*-
%%=============================================================================
%% Copyright (C) 2011 by Denys Duchier
%%
%% This program is free software: you can redistribute it and/or modify it
%% under the terms of the GNU Lesser General Public License as published by the
%% Free Software Foundation, either version 3 of the License, or (at your
%% option) any later version.
%%
%% This program is distributed in the hope that it will be useful, but WITHOUT
%% ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
%% FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
%% more details.
%%
%% You should have received a copy of the GNU Lesser General Public License
%% along with this program. If not, see <http://www.gnu.org/licenses/>.
%%=============================================================================
:- use_module(library(gecode)).
:- use_module(library(maplist)).
% use alldiff constraints
queens(N, Solution) :-
Space := space,
length(Queens, N),
Queens := intvars(Space,N,1,N),
Space += distinct(Queens),
foldl(inc, Queens, Inc, 0, _),
foldl(dec, Queens, Dec, 0, _),
Space += distinct(Inc,Queens),
Space += distinct(Dec,Queens),
Space += branch(Queens, 'INT_VAR_SIZE_MIN', 'INT_VAL_MIN'),
SolSpace := search(Space),
Solution := val(SolSpace,Queens).
inc(_, I0, I0, I) :-
I is I0+1.
dec(_, I0, I0, I) :-
I is I0-1.
%
% Using gecode linear constraints for diagonals.
%
lqueens(N, Solution) :-
Space := space,
length(Queens, N),
Queens := intvars(Space,N,1,N),
Space += distinct(Queens),
lconstrain( Queens, Space, 0),
Space += branch(Queens, 'INT_VAR_SIZE_MIN', 'INT_VAL_MIN'),
SolSpace := search(Space),
Solution := val(SolSpace,Queens).
lconstrain([], _, _).
lconstrain( [Q|Queens], Space, I0) :-
I is I0+1,
foldl(constrain(Q, I0, Space), Queens, I, _),
lconstrain( Queens, Space, I).
constrain(Q, I, Space, R, J, J1) :-
% Q+I != R+J, Q-I != R-J <=> Q-R != J-I, Q-R != I-J,
J1 is J+1,
Sum is I-J,
Diff is J-I,
Space += linear([1,-1], [Q,R], 'IRT_NQ', Diff),
Space += linear([1,-1], [Q,R], 'IRT_NQ', Sum).