https://gist.github.com/mtsmfm/4b8ffb53ffac055f5843

ramen.ml

(*
行列のできるラーメン屋 ESM オフラインどう書くの問題を OCaml で解いてみたやつ
記事: http://mtsmfm.github.io/2015/10/22/esm-doukaku.html
問題: https://gist.github.com/mtsmfm/4b8ffb53ffac055f5843
*)

open Core

type state_t = Empty | Waiting | Eating | Resting

let seats = [(1, Empty); (2, Empty); (3, Empty); (4, Empty); (5, Empty); (6, Empty); (7, Empty); (8, Empty)]

let cycle seats = List.append (List.drop seats 1) (List.take seats 1)

let get_number = fst

let is_empty = function (_, Empty) -> true | _ -> false

let to_int_list num_str = String.to_list num_str |> List.map ~f:Char.get_digit_exn

let to_bin = function (_, Empty) -> 0 | _ -> 1

let succ = function
  | (n, Empty) -> (n, Empty)
  | (n, Waiting) -> (n, Eating)
  | (n, Eating) -> (n, Resting)
  | (n, Resting) -> (n, Empty)

let rec rotate n seats =
  let seats = List.map ~f:succ seats in
  let rec loop n seats =
    let parts = List.take seats n in
    if (List.for_all ~f:is_empty parts) then
      List.drop seats n |>
      List.append (List.map ~f:(fun s -> ((get_number s), Waiting)) parts) |>
      List.sort ~cmp:(fun x y -> get_number x - get_number y)
    else
      if (List.hd_exn parts |> get_number = 8) then
        rotate n (cycle seats)
      else
        loop n (cycle seats)
  in
  loop n seats

let solve input =
  to_int_list input |>
  List.fold_left ~init:seats ~f:(Fn.flip rotate) |>
  List.map ~f:to_bin |>
  List.map ~f:Int.to_string |>
  String.concat

let test input output =
  assert (solve input = output)

let () =
  test "3316" "11111110";;
  test "3342153" "11111111";;
  test "8" "11111111";;
  test "232624" "11110110";;
  test "1" "10000000";;
  test "224673432" "11111000";;
  test "123464334" "11111110";;
  test "44372332" "11111111";;
  test "2344" "11111111";;
  test "6448476233" "11111100";;
  test "4345174644" "11111111";;
  test "77743" "11111110";;
  test "2136524281" "10000000";;
  test "344373" "11100000";;
  test "434226" "11111111";;
  test "7433223" "11111110";;
  test "2246534" "11110111";;
  test "634" "11111110";;
  test "2222" "11111100";;
  test "2442343238" "11111111";;
  test "7243344" "11111111";;
  test "26147234" "10111111";;
  test "34424" "10011111";;
  test "6334" "11011111";;
  test "3828342" "11011110";;
  test "4431" "11110000";;
  test "2843212125" "11111111";;
  test "333336482" "11000000";;
  test "374" "11110000";;
  test "4382333" "11100111";;