2024 day 14 part 1

bin/day2414.ml

@@ -0,0 +1,51 @@
+module IntMap = Map.Make (Int)
+
+let parse_robot s =
+  let re =
+    Str.regexp {|p=\(-?[0-9]+\),\(-?[0-9]+\) v=\(-?[0-9]+\),\(-?[0-9]+\)|}
+  in
+  let _ = Str.search_forward re s 0 in
+  ( ( int_of_string (Str.matched_group 1 s),
+      int_of_string (Str.matched_group 2 s) ),
+    ( int_of_string (Str.matched_group 3 s),
+      int_of_string (Str.matched_group 4 s) ) )
+
+let parse_robots = List.map parse_robot
+let robots_of_file fname = Aoc.strings_of_file fname |> parse_robots
+let width = 101
+let height = 103
+let secs = 100
+
+let normalize_velocity (p, (dx, dy)) =
+  (p, ((dx + width) mod width, (dy + height) mod height))
+
+let calc_pos_after secs ((x, y), (dx, dy)) =
+  let x' = (x + (secs * dx)) mod width in
+  let y' = (y + (secs * dy)) mod height in
+  (x', y')
+
+let in_a_quadrant (x, y) = x <> width / 2 && y <> height / 2
+let update_count = function None -> Some 1 | Some x -> Some (x + 1)
+
+let get_quadrant (x, y) =
+  if x < width / 2 && y < height / 2 then 1
+  else if x > width / 2 && y < height / 2 then 2
+  else if x < width / 2 && y > height / 2 then 4
+  else if x > width / 2 && y > height / 2 then 3
+  else failwith "get_quadrant"
+
+let loc_counts map p =
+  let idx = get_quadrant p in
+  IntMap.update idx update_count map
+
+let part robots =
+  let counts =
+    robots
+    |> List.map normalize_velocity
+    |> List.map (calc_pos_after secs)
+    |> List.filter in_a_quadrant
+    |> List.fold_left loc_counts IntMap.empty
+  in
+  IntMap.fold (fun _ v acc -> acc * v) counts 1
+
+let _ = Aoc.main robots_of_file [ (string_of_int, part) ]

bin/dune

@@ -12,7 +12,8 @@
   day2410
   day2411
   day2412
-  day2413)
+  day2413
+  day2414)
  (names
   day2401
   day2402
@@ -26,5 +27,6 @@
   day2410
   day2411
   day2412
-  day2413)
+  day2413
+  day2414)
  (libraries str aoc))