Advent of code

day_8.ml

open Core;;

let s = {|nop +0
acc +1
jmp +4
acc +3
jmp -3
acc -99
acc +1
jmp -4
acc +6
|};;

let s = In_channel.read_all "input.txt" |> String.strip;;

let code = s 
  |> String.strip
  |> String.split ~on:'\n'
  |> List.map ~f:(fun l -> 
    let [instr; count] = String.split ~on:' ' l in
    (instr, int_of_string count))
  |> List.to_array;;



let run code = 
  let visited = Array.create ~len:(Array.length code) false in
  let rec loop i acc =
    if visited.(i) then
      acc
    else begin
      visited.(i) <- true;
      match Array.get code i with
      | ("nop", _) -> loop (i + 1) acc
      | ("acc", n) -> loop (i + 1) (acc + n)
      | ("jmp", n) -> loop (i + n) acc end in
  loop 0 0;;

run code;;

let option_or v ~alt = 
  match v with 
  | Some _ -> v
  | None -> alt ();;


let run code =
  let rec loop i acc visited switched = 
    if i >= Array.length code then
     Some acc
    else if visited.(i) then
     None
    else begin
      visited.(i) <- true;                        
      (if not switched then
        match Array.get code i with
        | ("nop", n) -> loop (i + n) acc (Array.copy visited) true
        | ("acc", n) -> None
        | ("jmp", _) -> loop (i + 1) acc (Array.copy visited) true
      else None) 
      |> option_or ~alt:(fun _ ->
      match Array.get code i with
      | ("nop", _) -> loop (i + 1) acc visited switched
      | ("acc", n) -> loop (i + 1) (acc + n) visited switched
      | ("jmp", n) -> loop (i + n) acc visited switched)
    end in
  loop 0 0 (Array.create ~len:(Array.length code) false) false;;

run start;;