Write a program to solve 4-Queens problem
💻 Solution
week6.pl/* Description:
In the 4 Queens problem the object is to place 4 queens on a chessboard in such a way that no queens can capture a piece. This means that no two queens may be placed on the same row, column, or diagonal.
*/
% Domains:
queen = q(integer, integer)
queens = queen*
freelist = integer*
board = board(queens, freelist, freelist, freelist, freelist)
% Predicates:
nondeterm placeN(integer, board, board)
nondeterm place_a_queen(integer, board, board)
nondeterm nqueens(integer)
nondeterm makelist(integer, freelist)
nondeterm findandremove(integer, freelist, freelist)
nextrow(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)):-
nextrow(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]) :-
N1=N-1,makelist(N1,Rest).
nextrow(Row,[Row|Rest],Rest).📤 Output
w6.txt% Goal
nqueens(4),nl.
board([q(1,2),q(2,4),q(3,1),q(4,3),[],[],[7,4,1],[7,4,1])
yes