advent_of_code_2024/2/solve_1.ml

open Stdio
open Str


let rec construct_list l1=
  let line = In_channel.input_line In_channel.stdin in
  match line with
  | None -> l1
  | Some x -> let report = List.map int_of_string (Str.split (regexp {| |}) x) in
              construct_list (report::l1)
;;

let rec is_safe status l = match status with
| "ko"         -> false
| "increasing" -> (match l with
                              | a :: b :: tl -> if ( (a < b) && ((abs (a - b)) < 4)) then (is_safe "increasing" (b::tl)) else (is_safe "ko" [])
                              | _ :: [] | [] -> is_safe "ok" [])
| "decreasing" -> (match l with
                              | a :: b :: tl -> if ( (a > b) && ((abs (a - b)) < 4)) then (is_safe "decreasing" (b::tl)) else (is_safe "ko" [])
                              | _ :: [] | [] -> is_safe "ok" [])
| "init"       -> (match l with
                              | a :: b :: tl -> if ((abs (a - b)) < 4) then 
                                                 (if (a < b) then (is_safe "increasing" (b::tl)) 
                                                  else 
                                                    (if (a == b) then (is_safe "ko" [])
                                                     else (is_safe "decreasing" (b::tl)))) 
                                                else 
                                                  (is_safe "ko" []) 
                              | _ :: [] | [] -> is_safe "ok" [])
| _            -> true (*any other value is considered ok*)
;;

let rec solve accum = function
  | hd :: tl -> if (is_safe "init" hd) then solve (accum + 1) tl else solve accum tl
  | [] -> accum
;;

let () =
  let li = construct_list [] in
    printf "Total: %d\n" (solve 0 li)