Advent of code 2015, day 1 answer

advent_day1.ml

let example = "" (* actual string of parentheses goes here *)

let accumulate_parens acc item =
    match item with
    | '(' -> acc + 1
    | ')' -> acc - 1
    | _ -> acc

let parse_parens x = String.fold x ~init:0
  ~f:accumulate_parens

let rec parse_parens_basement (lst: char List.t) (acc: int) (f: int -> char -> int) : int =
   match lst with
   | [] -> 0
   | x :: xs ->
     if acc = -1 then List.length xs else
     parse_parens_basement xs (f acc x) f


let () =
  let result = parse_parens example in
  printf "Example length: %d\n" (String.length example);
  printf "Final floor: %d\n" result;;

let () =
  let result = parse_parens_basement (String.to_list example) 0 accumulate_parens in
  printf "First basement pos: %d\n" (List.length (String.to_list example) - result);;