Tidy up 2024 day 15

bin/day2415.ml

@@ -1,5 +1,9 @@
-type grid = { grid : char array; width : int; height : int }
+type grid = { grid : char array; width : int }
+(** Grid type. Not our normal type as we want to use it in a mutable way. *)
 
+(** [grid_map fn strs] Returns a grid built up from the list of strings [strs].
+    [fn] takes a single string of all map characters and returns a string with
+    the appropriate replacements done. *)
 let grid_make posmap_fn strs =
   let grid =
     List.fold_left String.cat "" strs
@@ -7,9 +11,9 @@ let grid_make posmap_fn strs =
   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 }
-  { grid; width; height }
 
+(** [grid_print grid] prints [grid] to standard output. *)
 let[@warning "-32"] grid_print grid =
   Array.iteri
     (fun i c ->
@@ -17,11 +21,16 @@ let[@warning "-32"] grid_print grid =
       if i mod grid.width = grid.width - 1 then print_newline ())
     grid.grid
 
-let find_start_idx grid =
+(** [find_robot_idx grid] returns the index of the robot in grid. *)
+let find_robot_idx grid =
   match Array.find_index (( = ) '@') grid.grid with
-  | None -> failwith "find_start_idx"
+  | None -> failwith "find_robot_idx"
   | Some x -> x
 
+(** [instrs_of_file fname] reads from the file [fname] and returns a
+    [(grid, instrs)] pair. [grid] is a list of strings describing the initial
+    grid state. [instrs] is a list of characters giving movement instructions.
+*)
 let instrs_of_file fname =
   let strs = Aoc.strings_of_file fname in
   let rec impl acc = function
@@ -32,19 +41,29 @@ let instrs_of_file fname =
   let grid, moves = impl [] strs in
   (grid, List.fold_left String.cat "" moves |> String.to_seq |> List.of_seq)
 
-let rec move_robot_x grid i di =
+(** [move_x grid i di] moves the object in [grid] at [i] to [i + di] if
+    possible, returning the new location of the object (either [i] or [i + di]).
+    This assumes a horizontal movement of one step. *)
+let rec move_x grid i di =
+  assert (di == -1 || di == 1);
+  assert (i >= 0 && i <= Array.length grid.grid);
   match grid.grid.(i + di) with
   | '#' -> i
   | 'O' | '[' | ']' ->
-      if move_robot_x grid (i + di) di = i + di then i
+      if move_x grid (i + di) di = i + di then i else move_x grid i di
-      else move_robot_x grid i di
   | '.' ->
       grid.grid.(i + di) <- grid.grid.(i);
       grid.grid.(i) <- '.';
       i + di
-  | _ -> failwith "move_robot_x"
+  | _ -> failwith "move_x"
 
+(** [can_move_y grid i di] returns true if and only if it is possible to move
+    whatever is at [i] to [i + di] in [grid]. If [i + di] is full it recursively
+    checks to see if that can be moved as well. [di] must be a vertical
+    movement. *)
 let rec can_move_y grid i di =
+  assert (i >= 0 && i < Array.length grid.grid);
+  assert (di = grid.width || di = -grid.width);
   match grid.grid.(i + di) with
   | '#' -> false
   | '.' -> true
@@ -53,10 +72,15 @@ let rec can_move_y grid i 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 =
+(** [move_x grid i di] moves the object in [grid] at [i] to [i + di] if
+    possible, returning the new location of the object (either [i] or [i + di]).
+    This assumes a vertical movement of one step. *)
+let move_y grid i di =
+  assert (i >= 0 && i < Array.length grid.grid);
+  assert (di = grid.width || di = -grid.width);
   let rec do_move i =
     match grid.grid.(i + di) with
-    | '#' -> failwith "move_robot_y.do_move #"
+    | '#' -> failwith "move_y.do_move #"
     | '.' ->
         grid.grid.(i + di) <- grid.grid.(i);
         grid.grid.(i) <- '.'
@@ -71,27 +95,31 @@ let move_robot_y grid i di =
         do_move (i + di - 1);
         do_move (i + di);
         do_move i
-    | _ -> failwith "move_robot_y.do_move"
+    | _ -> failwith "move_y.do_move"
   in
   if can_move_y grid i di then (
     do_move i;
     i + di)
   else i
 
+(** [process_move grid robot dir] attempts to move robot at idx [robot] in
+    [grid] in direction. Returns location of robot after attempt. *)
 let process_move grid robot dir =
-  (*grid_print grid;
-  Printf.printf "\nMove: %c\n" dir;*)
   match dir with
-  | '^' -> move_robot_y grid robot ~-(grid.width)
+  | '^' -> move_y grid robot (-grid.width)
-  | 'v' -> move_robot_y grid robot grid.width
+  | 'v' -> move_y grid robot grid.width
-  | '<' -> move_robot_x grid robot ~-1
+  | '<' -> move_x grid robot ~-1
-  | '>' -> move_robot_x grid robot 1
+  | '>' -> move_x grid robot 1
   | _ -> failwith "process_move"
 
+(** [process_moves grid robot lst] Attempts each move in [lst] in turn given a
+    [grid] and initial starting position of the robot [robot]. Returns the
+    [grid]. *)
 let rec process_moves grid robot = function
-  | [] -> grid
+  | [] -> ()
   | h :: t -> process_moves grid (process_move grid robot h) t
 
+(** [calc_score grid] returns the score for [grid]. *)
 let calc_score grid =
   Array.mapi
     (fun idx c ->
@@ -101,6 +129,8 @@ let calc_score grid =
     grid.grid
   |> Array.fold_left ( + ) 0
 
+(** [expand_grid str] given an input [str] returns the output grid string for
+    part 2. *)
 let expand_grid str =
   let b = Buffer.create (String.length str * 2) in
   let add_c = function
@@ -113,10 +143,12 @@ let expand_grid str =
   String.iter add_c str;
   Buffer.contents b
 
+(** [part posmap_fn (grid, moves)] executes the [moves] in [grid] having first
+    applied [posmap_fn] to grid. *)
 let part posmap_fn (grid, moves) =
   let grid = grid_make posmap_fn grid in
-  let robot = find_start_idx grid in
+  let robot = find_robot_idx grid in
-  let _ = process_moves grid robot moves in
+  process_moves grid robot moves;
   (*grid_print grid;*)
   calc_score grid