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![open List
let rec transpose = function [] | [] :: _ -> [] | r -> (map hd r) :: transpose (map tl r)
let problems = In_channel.input_lines stdin |> map String.to_seq |> map of_seq |> rev
let ops = hd problems |> filter_map (function '+' -> Some 0 | '*' -> Some 1 | _ -> None)
let numbers = tl problems |> rev |> transpose
|> map (fun l -> to_seq l |> String.of_seq |> String.trim |> int_of_string_opt)
let total = fold_left
(fun (ops, ttl, acc) -> function
| Some n -> ops, ttl, if hd ops = 0 then n + acc else n * acc
| None -> tl ops, ttl + acc, hd (tl ops))
(ops, 0, hd ops) numbers
|> fun (_, ttl, acc) -> ttl + acc
let () = Printf.printf "%d\n" total](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:7g4ic3vzf6ts42dmpy5usg4l/bafkreigldqicikmgctcwazeorm46thslbcqjemiqydcavfa5qohzqxdewy)
![let num = ['0' - '9']+
(* `num` is now as alias for a regexp that matches integer *)
rule dial passwd pos = parse
(* we define a new lexing rule `dial` which takes two arguments:
- `passwd` which is our accumulator, and
- `pos` our current position *)
| ['L' 'R'] num+ as rot {
(* when we read 'L' or 'R' followed by a num, call this string `rot` *)
let dir, clicks = rot.[0], int_of_string Str.(string_after rot 1) in
(* parsing the string as a char for direction and an int for clicks *)
let new_pos = ((if dir = 'L' then (-) else (+)) pos clicks + 100) mod 100 in
(* computing the new position by either adding or subtracting the
number of clicks depeding on the direction *)
dial (passwd + Bool.to_int (new_pos = 0)) new_pos lexbuf
(* recursive call to read the rest of the file starting from the
new position and accumulating a zero crossing if necessary *)
}
| '\n' { dial passwd pos lexbuf } (* on newlines, recursive call to go read the next line *)
| eof { passwd } (* at the end of the file, return the accumulator *)
{
Printf.printf "%d\n" (dial 0 50 (Lexing.from_channel stdin))
(* call our lexer from OCaml with initial position at 50 *)
}](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:7g4ic3vzf6ts42dmpy5usg4l/bafkreidstwba7oh6j73ap4u3rptvuqt3zn3tmd7hqct5q6ysxcdzg56nlm)
