aoc23/13/part1.pl

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2023-12-13 02:29:06 -06:00
:- use_module(library(pio)).
:- initialization(main, main).
main([FileName|_]) :-
input(FileName, Blocks),
convlist(vert_reflect, Blocks, Vs),
convlist(horz_reflect, Blocks, Hs),
sum_list(Vs, V),
sum_list(Hs, H),
Answer is 100*V + H,
writef('Answer=%t\n', [Answer]).
vert_reflect(Block, N) :- reflect(Block, N).
horz_reflect(Block, N) :- maplist({N}/[Row]>>(reflect(Row, N)), Block).
reflect(Items, N) :- perfect_reflect(Items, N).
reflect(Items, N) :-
append(SubItems, [_|_], Items),
perfect_reflect(SubItems, N).
reflect(Items, N) :-
append(Prefix, SubItems, Items),
perfect_reflect(SubItems, SubN),
length(Prefix, Len), N is SubN + Len.
% reflect right down the middle. N is half list length.
perfect_reflect([A, A], 1).
perfect_reflect(Items, N) :-
append([[Item], OtherItems, [Item]], Items),
perfect_reflect(OtherItems, N_sub1),
N is N_sub1 + 1.
input(FileName, Blocks) :- phrase_from_file(blocks(Blocks), FileName).
blocks([]) --> eos, !.
blocks([Block|Blocks]) --> block(Block), blocks(Blocks).
block([Line]) --> line(Line), ("\n"; eos), !.
block([Line|Lines]) --> line(Line), block(Lines).
line([]) --> ("\n"; eos), !.
line([#|Chars]) --> "#", line(Chars).
line([o|Chars]) --> ".", line(Chars).
eos([], []).