66 lines
2.0 KiB
OCaml
66 lines
2.0 KiB
OCaml
(** [towels_of_strings lst] returns a pair containing a list of available towels
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and a list of patterns wanted. *)
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let towels_of_strings = function
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| h :: "" :: t ->
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let re = Str.regexp "[, ]+" in
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let h = Str.split re h in
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(h, t)
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| _ -> failwith "towels_of_strings"
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let towels_of_file fname = Aoc.strings_of_file fname |> towels_of_strings
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let memo = Hashtbl.create 1000
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let rec memoize_has_pattern pattern towels =
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let pattern_len = String.length pattern in
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let rec has_pattern = function
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| [] -> false
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| h :: t ->
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let towel_len = String.length h in
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if String.starts_with ~prefix:h pattern then
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memoize_has_pattern
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(String.sub pattern towel_len (pattern_len - towel_len))
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towels
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|| has_pattern t
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else has_pattern t
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in
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match Hashtbl.find_opt memo pattern with
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| Some x -> x
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| None ->
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let x = if pattern_len = 0 then true else has_pattern towels in
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Hashtbl.add memo pattern x;
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x
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let has_match towels pattern = memoize_has_pattern pattern towels
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let memo2 = Hashtbl.create 1000
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let rec memoize_count_matches pattern towels =
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let pattern_len = String.length pattern in
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let rec has_pattern = function
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| [] -> 0
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| h :: t ->
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let towel_len = String.length h in
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if String.starts_with ~prefix:h pattern then
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memoize_count_matches
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(String.sub pattern towel_len (pattern_len - towel_len))
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towels
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+ has_pattern t
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else has_pattern t
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in
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match Hashtbl.find_opt memo2 pattern with
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| Some x -> x
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| None ->
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let x = if pattern_len = 0 then 1 else has_pattern towels in
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Hashtbl.add memo2 pattern x;
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x
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let count_matches towels pattern = memoize_count_matches pattern towels
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let part1 (towels, patterns) =
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List.filter (has_match towels) patterns |> List.length
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let part2 (towels, patterns) =
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List.map (count_matches towels) patterns |> List.fold_left ( + ) 0
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let _ =
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Aoc.main towels_of_file [ (string_of_int, part1); (string_of_int, part2) ]
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