2024 day 16 part 1

bin/day2416.ml

@@ -0,0 +1,58 @@
+let find grid c =
+  match Aoc.Grid.idx_from_opt grid 0 c with
+  | None -> failwith "find"
+  | Some idx -> Aoc.Grid.pos_of_idx grid idx
+
+let input_of_file fname =
+  let grid = Aoc.Grid.of_file fname in
+  let start_state = (find grid 'S', (1, 0)) in
+  (grid, start_state)
+
+let rec dijkstra visit check_end states =
+  let compare_costs (lhs, _) (rhs, _) = compare lhs rhs in
+  match states with
+  | [] -> failwith "dijkstra"
+  | (cost, state) :: t ->
+      if check_end state then cost
+      else
+        let new_states =
+          visit cost state |> List.sort compare_costs
+          |> List.merge compare_costs t
+        in
+        dijkstra visit check_end new_states
+
+let visited_idx grid (p, (dx, dy)) =
+  let add =
+    match (dx, dy) with
+    | 1, 0 -> 0
+    | 0, 1 -> 1
+    | -1, 0 -> 2
+    | 0, -1 -> 3
+    | _ -> failwith "visited_idx"
+  in
+  (Aoc.Grid.idx_of_pos grid p * 4) + add
+
+let has_visited grid visited_grid state = visited_grid.(visited_idx grid state)
+
+let mark_visited grid visited_grid state =
+  visited_grid.(visited_idx grid state) <- true
+
+let visit grid visited_grid cost ((((x, y) as p), (dx, dy)) as state) =
+  if has_visited grid visited_grid state then []
+  else if Aoc.Grid.get_by_pos grid p = '#' then []
+  else (
+    Printf.printf "%d %d %d %d %d\n" cost x y dx dy;
+    mark_visited grid visited_grid state;
+    [
+      (cost + 1, ((x + dx, y + dy), (dx, dy)));
+      (cost + 1000, (p, (-dy, dx)));
+      (cost + 1000, (p, (dy, -dx)));
+    ])
+
+let check_end grid (p, _) = Aoc.Grid.get_by_pos grid p = 'E'
+
+let part (grid, start_state) =
+  let visited_grid = Array.make (Aoc.Grid.length grid * 4) false in
+  dijkstra (visit grid visited_grid) (check_end grid) [ (0, start_state) ]
+
+let _ = Aoc.main input_of_file [ (string_of_int, part) ]