71 lines
2.1 KiB
OCaml
71 lines
2.1 KiB
OCaml
(** [nums_from_string s] takes a string of space separated integers and gives
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back a list of the integers. *)
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let nums_from_string s =
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List.map int_of_string (Str.split (Str.regexp " +") s);;
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(** [pair_nums_from_string s] takes a string of two numbers separated by
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whitespace and returns the pair of the numbers *)
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let pair_nums_from_string s =
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match (nums_from_string s) with
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| h :: h' :: [] -> (h, h')
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| _ -> raise (Invalid_argument "pair_nums_from_string")
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(** [unzip lst] takes a list of pairs and returns a pair of lists. *)
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let unzip lst =
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let rec impl acc acc' = function
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| (h, h') :: t -> impl (h :: acc) (h' :: acc') t
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| _ -> (acc, acc')
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in
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impl [] [] lst
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(** [pairs_from_channel ch] returns the list of pairs given on the channel
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*)
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let pairs_from_channel ch =
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let rec impl acc =
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try (impl ((input_line ch) :: acc)) with
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| End_of_file -> acc
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in
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impl [] |> List.map pair_nums_from_string
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(** [pairs_from_file fname] returns the list of pairs given in the file *)
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let pairs_from_file fname =
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try
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let ch = open_in fname in
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pairs_from_channel ch
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with
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| _ -> failwith "pairs_from_file"
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(** [distance a b] returns the absolute difference between [a] and [b]. *)
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let distance a b =
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abs (a - b)
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let day2401a fname =
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let (a, b) = unzip (pairs_from_file fname) in
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let d = List.map2 distance (List.sort Int.compare a) (List.sort Int.compare b) in
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List.fold_left ( + ) 0 d
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(** [count lst n] counts the number of times [n] appears as an element in [lst].
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*)
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let count lst n =
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List.fold_left (fun acc x -> if x = n then (acc + 1) else acc) 0 lst
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let day2401b fname =
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let (a, b) = unzip (pairs_from_file fname) in
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List.map (count b) a |>
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List.map2 ( * ) a |>
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List.fold_left ( + ) 0
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let _ = try
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begin
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match Sys.argv with
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| [|_; fname|] ->
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Printf.printf "Part 1 = %d\n" (day2401a fname);
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Printf.printf "Part 2 = %d\n" (day2401b fname);
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| _ ->
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Printf.printf "Usage: day2401 <fname>\n";
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exit 1
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end
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with
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| e ->
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Printf.printf "An error occured: %s\n" (Printexc.to_string e);
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exit 1 |