domains
queen
= q(integer,integer)
queens=queen*
freelist
= integer*
board=board(queens,freelist,freelist,freelist,freelist)
predicates
placeN(integer,board,board)
place_a_queen(integer,board,board)
nqueens(integer)
makelist(integer,freelist)
findandremove(integer,freelist,freelist)
clauses
nqueens(N):-
makelist(N,L),Diagonal=N*2-1,makelist(Diagonal,LL),
placeN(N,board([],L,L,LL,LL),Final),write(Final).
placeN(_,board(D,[],[],D1,D2),board(D,[],[],D1,D2)):-!.
placeN(N,Board1,Result):-
place_a_queen(N,Board1,Board2),
placeN(N,Board2,Result).
place_a_queen(N,board(Queens,Rows,Columns,Diag1,Diag2),
board([q(R,C)|Queens],NewR,NewC,NewD1,NewD2)):-
findandremove(R,Rows,NewR),
findandremove(C,Columns,NewC),
D1=N+C-R,findandremove(D1,Diag1,NewD1),
D2=R+C-1,findandremove(D2,Diag2,NewD2).
findandremove(X,[X|Rest],Rest).
findandremove(X,[Y|Rest],[Y|Tail]):-
findandremove(X,Rest,Tail).
makelist(1,[1]).
makelist(N,[N|Rest]):-
N>0,N1=N-1,makelist(N1,Rest).
Output:-
