2024 day 15 part 2

bin/day2415.ml

@@ -1,17 +1,15 @@
 type grid = { grid : char array; width : int; height : int }
 
-let grid_make strs =
+let grid_make posmap_fn strs =
   let grid =
-    List.fold_left String.cat "" strs |> String.to_seq |> Array.of_seq
+    List.fold_left String.cat "" strs
+    |> posmap_fn |> String.to_seq |> Array.of_seq
   in
   let height = List.length strs in
   let width = Array.length grid / height in
+  Printf.printf "width %d height %d \n" width height;
   { grid; width; height }
 
-let grid_copy grid = { grid with grid = Array.copy grid.grid }
-let grid_height grid = grid.height
-let[@warning "-32"] grid_length grid = grid.width * grid.height
-
 let[@warning "-32"] grid_print grid =
   Array.iteri
     (fun i c ->
@@ -32,28 +30,62 @@ let instrs_of_file fname =
     | h :: t -> impl (h :: acc) t
   in
   let grid, moves = impl [] strs in
-  let grid = grid_make grid in
-  ( grid,
-    List.fold_left String.cat "" moves |> String.to_seq |> List.of_seq,
-    find_start_idx grid )
+  (grid, List.fold_left String.cat "" moves |> String.to_seq |> List.of_seq)
 
-let rec move_robot grid i di =
+let rec move_robot_x grid i di =
   match grid.grid.(i + di) with
   | '#' -> i
-  | 'O' ->
-      if move_robot grid (i + di) di = i + di then i else move_robot grid i di
+  | 'O' | '[' | ']' ->
+      if move_robot_x grid (i + di) di = i + di then i
+      else move_robot_x grid i di
   | '.' ->
       grid.grid.(i + di) <- grid.grid.(i);
       grid.grid.(i) <- '.';
       i + di
-  | _ -> failwith "move_robot"
+  | _ -> failwith "move_robot_x"
+
+let rec can_move_y grid i di =
+  match grid.grid.(i + di) with
+  | '#' -> false
+  | '.' -> true
+  | 'O' -> can_move_y grid (i + di) di
+  | '[' -> can_move_y grid (i + di) di && can_move_y grid (i + di + 1) di
+  | ']' -> can_move_y grid (i + di - 1) di && can_move_y grid (i + di) di
+  | _ -> failwith "can_move_y"
+
+let move_robot_y grid i di =
+  let rec do_move i =
+    match grid.grid.(i + di) with
+    | '#' -> failwith "move_robot_y.do_move #"
+    | '.' ->
+        grid.grid.(i + di) <- grid.grid.(i);
+        grid.grid.(i) <- '.'
+    | 'O' ->
+        do_move (i + di);
+        do_move i
+    | '[' ->
+        do_move (i + di);
+        do_move (i + di + 1);
+        do_move i
+    | ']' ->
+        do_move (i + di - 1);
+        do_move (i + di);
+        do_move i
+    | _ -> failwith "move_robot_y.do_move"
+  in
+  if can_move_y grid i di then (
+    do_move i;
+    i + di)
+  else i
 
 let process_move grid robot dir =
+  (*grid_print grid;
+  Printf.printf "\nMove: %c\n" dir;*)
   match dir with
-  | '^' -> move_robot grid robot ~-(grid_height grid)
-  | 'v' -> move_robot grid robot (grid_height grid)
-  | '<' -> move_robot grid robot ~-1
-  | '>' -> move_robot grid robot 1
+  | '^' -> move_robot_y grid robot ~-(grid.width)
+  | 'v' -> move_robot_y grid robot grid.width
+  | '<' -> move_robot_x grid robot ~-1
+  | '>' -> move_robot_x grid robot 1
   | _ -> failwith "process_move"
 
 let rec process_moves grid robot = function
@@ -63,13 +95,31 @@ let rec process_moves grid robot = function
 let calc_score grid =
   Array.mapi
     (fun idx c ->
-      if c = 'O' then (idx mod grid.width) + (100 * (idx / grid.height)) else 0)
+      if c = 'O' || c = '[' then
+        (idx mod grid.width) + (100 * (idx / grid.width))
+      else 0)
     grid.grid
   |> Array.fold_left ( + ) 0
 
-let part (grid, moves, robot) =
-  let grid = grid_copy grid in
+let expand_grid str =
+  let b = Buffer.create (String.length str * 2) in
+  let add_c = function
+    | '#' -> Buffer.add_string b "##"
+    | 'O' -> Buffer.add_string b "[]"
+    | '.' -> Buffer.add_string b ".."
+    | '@' -> Buffer.add_string b "@."
+    | _ -> failwith "expand_grid"
+  in
+  String.iter add_c str;
+  Buffer.contents b
+
+let part posmap_fn (grid, moves) =
+  let grid = grid_make posmap_fn grid in
+  let robot = find_start_idx grid in
   let _ = process_moves grid robot moves in
+  (*grid_print grid;*)
   calc_score grid
 
-let _ = Aoc.main instrs_of_file [ (string_of_int, part) ]
+let _ =
+  Aoc.main instrs_of_file
+    [ (string_of_int, part Fun.id); (string_of_int, part expand_grid) ]