part 6

6/main.ml

@@ -0,0 +1,140 @@
+open Printf;;
+open String;;
+
+let rec list_of_lines in_file =
+  try
+    let line = input_line in_file in
+    line :: list_of_lines(in_file)
+  with End_of_file ->
+    close_in in_file;
+    []
+
+let file_to_2d_array in_file =
+  let lines = list_of_lines in_file in
+  let size_x = length @@ List.hd lines in
+  let size_y = List.length lines in
+  let arr = Array.make_matrix size_x size_y '?' in
+  List.iteri (fun j line -> String.iteri (fun i c -> arr.(j).(i) <- c) line) lines;
+  arr
+
+let rec find_index_inner elem arr pos =
+  try
+    if arr.(pos) = elem then
+      Some pos
+    else
+      find_index_inner elem arr (pos + 1)
+  with Invalid_argument _ -> None
+
+let find_index elem arr =
+  find_index_inner elem arr 0
+
+let rec find_index_2d_inner elem arr pos =
+  try
+    match find_index elem arr.(pos) with
+    | Some pos_x -> Some (pos_x, pos)
+    | None -> find_index_2d_inner elem arr (pos + 1)
+  with Invalid_argument _ -> None
+
+let find_index_2d elem arr =
+  find_index_2d_inner elem arr 0
+
+
+  let find_all_indices_of elem arr =
+    arr |> Array.to_seq
+        |> Seq.mapi (fun i x -> (i, x))
+        |> Seq.filter_map (fun (i, x) -> if x = elem then Some i else None)
+  
+  let find_all_indices_of_2d elem arr =
+    arr |> Array.to_seq
+        |> Seq.mapi (fun j row -> Seq.map (fun i -> (i, j)) (find_all_indices_of elem row))
+        |> Seq.concat
+
+let find_guard_position arr =
+  arr |> find_index_2d '^' |> Option.get
+
+type dir =
+  | Up
+  | Down
+  | Left
+  | Right
+
+let get_new_pos guard_pos dir =
+  match dir with
+  | Up -> (fst guard_pos, snd guard_pos - 1)
+  | Down -> (fst guard_pos, snd guard_pos + 1)
+  | Left -> (fst guard_pos - 1, snd guard_pos)
+  | Right -> (fst guard_pos + 1, snd guard_pos)
+
+let turn_right dir =
+  match dir with
+  | Up -> Right
+  | Down -> Left
+  | Left -> Up
+  | Right -> Down
+
+let int_of_dir dir =
+  match dir with
+  | Up -> 0
+  | Down -> 1
+  | Left -> 2
+  | Right -> 3
+
+let guard_state_index pos dir =
+  Int.logor (fst pos) (
+  Int.logor (Int.shift_left (snd pos) 12)
+            (Int.shift_left (int_of_dir dir) 24))
+
+module IntSet = Set.Make(Int)
+
+let rec rotate_until_can_move arr guard_pos dir =
+  let new_pos = get_new_pos guard_pos dir in
+  if arr.(snd new_pos).(fst new_pos) <> '#' then
+    dir
+  else
+    let new_dir = turn_right dir in
+    rotate_until_can_move arr guard_pos new_dir
+
+(* returns true if guard is able to complete the walk, false if guard falls into a cycle *)
+let rec guard_walk_inner arr previous_states guard_pos dir =
+  try
+    arr.(snd guard_pos).(fst guard_pos) <- 'X';
+    let guard_state_index = (guard_state_index guard_pos dir) in
+    if Option.is_some @@ IntSet.find_opt guard_state_index previous_states then
+      false
+    else
+      let new_previous_states = IntSet.add guard_state_index previous_states in
+      let new_dir = rotate_until_can_move arr guard_pos dir in
+      let new_pos = get_new_pos guard_pos new_dir in
+      guard_walk_inner arr new_previous_states new_pos new_dir
+  with Invalid_argument _ -> true
+
+let guard_walk arr guard_pos dir =
+  guard_walk_inner arr IntSet.empty guard_pos dir
+
+let count_2d value arr =
+  Array.fold_left 
+    (fun acc elem -> acc + 
+      Array.fold_left 
+        (fun acc2 elem2 -> acc2 + if elem2 = value then 1 else 0)
+        0 elem) 
+    0 arr
+
+let array_copy_2d arr =
+  Array.init (Array.length arr) (fun i -> Array.copy arr.(i))
+
+let try_block_guard arr guard_pos obstacle_pos =
+  let array_copy = array_copy_2d arr in
+  array_copy.(snd obstacle_pos).(fst obstacle_pos) <- '#';
+  not @@ guard_walk array_copy guard_pos Up
+
+let () =
+  let f = open_in "input.txt" in
+  let arr = file_to_2d_array f in
+  let guard_pos = find_guard_position arr in
+  let _ = guard_walk arr guard_pos Up in
+  let visited = List.of_seq (find_all_indices_of_2d 'X' arr) in
+  let result = List.length visited in
+  printf "%d\n%!" result;
+  let cycle_positions = List.filter (try_block_guard arr guard_pos) visited in
+  let result2 = List.length cycle_positions in
+  printf "%d\n" result2;

ocaml compilation is weird.txt

@@ -5,3 +5,6 @@ cmd /c "(ocamlc main.ml) && camlprog.exe"
 Libraries:
 ocamlfind ocamlc -linkpkg -package str main.ml && ./camlprog
 cmd /c "(ocamlfind ocamlc -linkpkg -package str main.ml) && camlprog.exe"
+
+Optimization:
+ocamlc can be replaced with ocamlopt to produce faster code but the compilation is slow