Prolog domino game

Question

i\'m making a game in prolog, with a given set of domino pieces, it should make a correct domino row using all the pieces in the initial set. we must use an inference system

Answer 1

Consider something like this:

% L1 is a list of domino pieces (of the form X-Y)
% L2 is L1 in domino order
domino_order(L1, L2) :-
    domino_order(L1, _, L2).

domino_order([], _, []) :- !.
domino_order(In, X, [X-Y | Out]) :-
    select(Piece, In, Remaining),
    swap_or_not(Piece, X-Y),
    domino_order(Remaining, Y, Out).

swap_or_not(X-Y, X-Y).
swap_or_not(X-Y, Y-X).

Usage:

?- domino_order([5-4, 1-2, 4-3, 2-3], Out).
Out = [5-4, 4-3, 3-2, 2-1] ;
Out = [1-2, 2-3, 3-4, 4-5] ;
false.