Split a list in half

Question

I need to define divide so that List [1,2,3,4,5] divides into:

a = [1,2,3}

b = [4,5]

I\'m getting an error that says \"

Answer 1

This is the most efficient solution conforming to your specification for most Prolog implementations:

divide(L, A, B) :-
    divide1(L, L, A, B).

divide1([], L, [], L).
divide1([_|T], [H|L], [H|A], B) :-
    divide2(T, L, A, B).

divide2([], L, [], L).
divide2([_|T], L, A, B) :-
    divide1(T, L, A, B).

If you don't mind which elements go into the sublists as far as they are of similar length (as in the solution from Konstantin Weitz post), then you can use :

divide([], [], []).
divide([H|T], [H|A], B) :- divide(T, B, A).