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/*-------------------------------------------------------------------------*/
/* 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).
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