routes.pl

/* Facts */
road(varrock, falador, 5).

road(lumbridge, varrock, 4). /* Cycle */
road(varrock, lumbridge, 4).

road(lumbridge, draynor, 2).
road(draynor, falador, 3).
road(falador, taverly, 2).
road(falador, portsarim, 3).
road(falador, rimmington, 2).
road(draynor, portsarim, 1).
road(portsarim, rimmington, 1).
road(taverly, catherby, 4).
road(catherby, camelot, 2).
road(camelot, ardougne, 4).
road(camelot, rellekka, 7).
road(varrock, wilderness, 10).


/* Rules */

/* Question1  is true if a route R of length N exists between town X and town Y */
route(X, Y, R, N) :- road(X, Y, N), R1 = [Y], R = [X|R1].
route(X, Y, R, N) :- road(X, Z, N1), route(Z, Y, R1, N2), \+ member(X, R1), R = [X | R1], N is N1+N2.


/* Question2  is true if the route R of length N between town X and town Y is the shortest route between X and Y */
/* shortest(X,Y,R,N):- .*/