:- module day1.
:- interface.
:- import_module basics.

:- pred run(part::in, lines::in, answer::out) is cc_multi.

:- implementation.
:- import_module list.
:- import_module maybe.

:- pragma no_determinism_warning(run/3).
run(one, Lines, int(det_head(go(Lines)))).
run(two, Lines, int(sum(take_upto(3, go(Lines))))).

:- func go(lines) = list(int).
go(Lines) =
  rev_sort(map(sum, gather(map(to_int_may, Lines)))).

:- func gather(list(maybe(T))) = list(list(T)).
gather(Xs) = Ys :- gather(Xs, Ys).

:- pred gather(list(maybe(T))::in, list(list(T))::out(non_empty_list)) is det.
gather([],            [[]]).
gather([no     | Xs], [[]       | Yss]) :- gather(Xs, Yss).
gather([yes(Y) | Xs], [[Y | Ys] | Yss]) :- gather(Xs, [Ys | Yss]).