/*-------------------------------------------------------------------------*/
/* Benchmark (Boolean) */
/* */
/* Name : bqueens.pl */
/* Title : N-queens problem */
/* Original Source: Daniel Diaz - INRIA France */
/* 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. */
/* The solution is a list [ [Que11,...,Que1N], ... ,[QueN1,...,QueNN] ] */
/* where Queij is 1 if the the is a queen on the ith line an jth row. */
/* */
/* Solution: */
/* N=4 [[0,0,1,0], [[0,1,0,0], */
/* [1,0,0,0], [0,0,0,1], */
/* [0,0,0,1], and [1,0,0,0], */
/* [0,1,0,0]] [0,0,1,0]] */
/* */
/* N=8 [[0,0,0,0,0,0,0,1], (first solution) */
/* [0,0,0,1,0,0,0,0], */
/* [1,0,0,0,0,0,0,0], */
/* [0,0,1,0,0,0,0,0], */
/* [0,0,0,0,0,1,0,0], */
/* [0,1,0,0,0,0,0,0], */
/* [0,0,0,0,0,0,1,0], */
/* [0,0,0,0,1,0,0,0]] */
/*-------------------------------------------------------------------------*/
q:- write('N ?'), read_integer(N),
statistics(runtime,_),
(bqueens(N,A),
write(A), nl %,
% fail
;
write('No more solutions'), nl),
statistics(runtime,[_,Y]),
write('time : '), write(Y), nl.
bqueens(N,A):-
create_array(N,N,A),
for_each_line(A,only1),
for_each_column(A,only1),
for_each_diagonal(A,N,N,atmost1),
!,
array_labeling(A).
:- include(array).
% interface with for_each_... procedures
array_prog(only1,L):-
fd_only_one(L).
array_prog(atmost1,L):-
fd_at_most_one(L).
:- initialization(q).
