dev/prolog/queens.pl

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/*-------------------------------------------------------------------------*/
/* Benchmark (Finite Domain) */
/* */
/* Name : queens.pl */
/* Title : N-queens problem */
/* Original Source: P. Van Hentenryck's book */
/* Adapted by : Daniel Diaz for GNU Prolog */
/* Date : January 1993 */
/* */
/* Put N queens on an NxN chessboard so that there is no couple of queens */
/* threatening each other. */
/* */
/* Solution: */
/* N=4 [2,4,1,3] */
/* N=8 [1,5,8,6,3,7,2,4] */
/* N=16 [1,3,5,2,13,9,14,12,15,6,16,7,4,11,8,10] */
/*-------------------------------------------------------------------------*/
q:- get_fd_labeling(Lab), write('N ?'), read_integer(N),
statistics(runtime,_),
queens(N,L,Lab), statistics(runtime,[_,Y]),
write(L), nl,
write('time : '), write(Y), nl.
queens(N,L,Lab):-
fd_set_vector_max(N),
length(L,N),
fd_domain(L,1,N),
safe(L),
lab(Lab,L).
safe([]).
safe([X|L]):-
noattack(L,X,1),
safe(L).
noattack([],_,_).
/*
% faster than the original PVH's version
noattack([Y|L],X,I):-
I1 is I+1,
noattack(L,X,I1),
diff(X,Y,I).
*/
noattack([Y|L],X,I):-
diff(X,Y,I),
I1 is I+1,
noattack(L,X,I1).
diff(X,Y,I):-
fd_tell(diff(X,Y,I)).
/*
diff(X,Y,I):-
X#\=Y,
X#\=Y+I,
X+I#\=Y.
*/
lab(normal,L):-
fd_labeling(L).
lab(ff,L):-
fd_labelingff(L).
get_fd_labeling(Lab):-
argument_counter(C),
get_labeling1(C,Lab).
get_labeling1(1,normal).
get_labeling1(2,Lab):-
argument_value(1,Lab).
:- initialization(q).