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|
(*
* SPDX-FileCopyrightText: Copyright 2025 Alexandre Jesus <https://adbjesus.com>
*
* SPDX-License-Identifier: GPL-3.0-or-later
*)
let parse_data ch =
In_channel.input_all ch
|> String.trim
|> String.split_on_char '\n'
|> List.mapi (fun i s -> (i, s))
|> List.to_seq
|> Seq.flat_map (fun (i, s) ->
String.to_seq s
|> Seq.mapi (fun j v -> (j, v = '@'))
|> Seq.filter_map (fun (j, p) -> if p then Some ((i, j), 0) else None))
|> Hashtbl.of_seq
let neighs =
[ (-1, -1); (-1, 0); (-1, 1); (0, -1); (0, 1); (1, -1); (1, 0); (1, 1) ]
let neighs (i, j) = List.map (fun (a, b) -> (i + a, j + b)) neighs
let count tbl k = (k, neighs k |> List.filter (Hashtbl.mem tbl) |> List.length)
let counts tbl = Hashtbl.to_seq_keys tbl |> Seq.map (count tbl)
let part1 ch =
parse_data ch
|> counts
|> Seq.filter (fun (_, v) -> v < 4)
|> Seq.length
|> Printf.printf "%d\n"
let part2 ch =
let tbl = parse_data ch |> counts |> Hashtbl.of_seq in
let rec fn acc s =
let test k =
match Hashtbl.find_opt tbl k with
| None -> None
| Some v when v = 4 ->
Hashtbl.remove tbl k;
Some k
| Some v ->
Hashtbl.replace tbl k (v - 1);
None
in
match s with
| [] -> acc
| h :: t ->
neighs h
|> List.filter_map test
|> List.fold_left (fun (acc, s) k -> (acc + 1, k :: s)) (acc, t)
|> fun (acc, s) -> fn acc s
in
Hashtbl.to_seq tbl
|> List.of_seq
|> List.filter_map (fun (k, v) ->
if v < 4 then (
Hashtbl.remove tbl k;
Some k)
else None)
|> (fun s -> fn (List.length s) s)
|> Printf.printf "%d\n"
|
