100 lines
3.4 KiB
OCaml
100 lines
3.4 KiB
OCaml
let string_to_char_list s =
|
|
s |> String.to_seq |> List.of_seq
|
|
let lines = Reuse.split "inputs/day04.txt" '\n'
|
|
let input = List.map string_to_char_list lines
|
|
|
|
let (>>=) = Option.bind ;;
|
|
let get_grid_pos (x: int) (y: int) (grid: char list list) : char option =
|
|
List.nth_opt grid x >>= fun sublist -> List.nth_opt sublist y
|
|
|
|
let get_neighbors (x: int) (y: int) (grid: char list list) : char option list =
|
|
let right_top = if y = 0 then None else get_grid_pos (x + 1) (y - 1) grid in
|
|
let left = if x = 0 then None else get_grid_pos (x - 1) y grid in
|
|
let left_bot = if x = 0 then None else get_grid_pos (x - 1) (y + 1) grid in
|
|
let top = if y = 0 then None else get_grid_pos x (y - 1) grid in
|
|
let left_top = if y = 0 || x = 0 then None else get_grid_pos (x - 1) (y - 1) grid in
|
|
[get_grid_pos (x + 1) y grid; get_grid_pos (x + 1) (y + 1) grid; right_top; left; left_bot; left_top;
|
|
get_grid_pos x (y + 1) grid; top]
|
|
|
|
let sum_papers (neighbors: char option list) : int =
|
|
List.length (List.filter (fun x -> x = Some '@') neighbors)
|
|
|
|
let update_grid_position (grid: char list list) (x, y: int * int) : char list list =
|
|
let update_row (row: char list) (y: int) : char list =
|
|
List.mapi (fun col_idx c -> if col_idx = y then '.' else c) row
|
|
in
|
|
List.mapi (fun row_idx row ->
|
|
if row_idx = x then update_row row y else row
|
|
) grid
|
|
|
|
let apply_to_all_positions (grid: char list list) (positions: (int * int) list) : char list list =
|
|
List.fold_left (fun current_grid (x,y) -> update_grid_position current_grid (x, y)) grid positions
|
|
|
|
let rec update_grid (grid: char list list) (acc : int) : int =
|
|
let result = ref acc in
|
|
let rows = List.length grid in
|
|
let cols = List.length (List.hd grid) in
|
|
let positions = ref [] in
|
|
for x = 0 to rows - 1 do
|
|
for y = 0 to cols - 1 do
|
|
let ats = sum_papers (get_neighbors x y grid) in
|
|
if get_grid_pos x y grid = Some '@' && ats < 4 then positions := [(x, y)] @ !positions;
|
|
result := !result + List.length !positions;
|
|
done;
|
|
done;
|
|
let new_grid = apply_to_all_positions grid !positions in
|
|
if new_grid = grid then acc else update_grid new_grid (acc + List.length !positions)
|
|
|
|
let solve_part1 (inputs: char list list) : int =
|
|
let result = ref 0 in
|
|
let rows = List.length inputs in
|
|
let cols = List.length (List.hd inputs) in
|
|
for x = 0 to rows - 1 do
|
|
for y = 0 to cols - 1 do
|
|
let ats = sum_papers (get_neighbors x y inputs) in
|
|
if get_grid_pos x y inputs = Some '@' && ats < 4 then result := !result + 1
|
|
done;
|
|
done;
|
|
!result
|
|
|
|
|
|
let solve_part2 (inputs: char list list) : int =
|
|
update_grid inputs 0
|
|
|
|
let day4_part1 : int =
|
|
solve_part1 input
|
|
|
|
let day4_part2 : int =
|
|
solve_part2 input
|
|
|
|
module Tests = struct
|
|
let test_input = "..@@.@@@@.
|
|
@@@.@.@.@@
|
|
@@@@@.@.@@
|
|
@.@@@@..@.
|
|
@@.@@@@.@@
|
|
.@@@@@@@.@
|
|
.@.@.@.@@@
|
|
@.@@@.@@@@
|
|
.@@@@@@@@.
|
|
@.@.@@@.@."
|
|
|
|
|
|
|
|
let run_tests () =
|
|
let test_lines = String.split_on_char '\n' test_input in
|
|
let test_input = List.map string_to_char_list test_lines in
|
|
|
|
let part1_result = solve_part1 test_input in
|
|
let part2_result = solve_part2 test_input in
|
|
if part1_result <> 13 then
|
|
failwith ("Day 4 Part 1 test failed: expected 13, got " ^ string_of_int part1_result);
|
|
|
|
if part2_result <> 43 then
|
|
failwith ("Day 4 Part 2 test failed: expected 43, got " ^ string_of_int part2_result);
|
|
|
|
Printf.printf "All day 4 tests passed!\n"
|
|
end
|
|
|
|
let () = Tests.run_tests()
|