Move IntPair and PosSet into Aoc library.

These are obviously generic enough and useful for the future that they
can be moved to a shared library.

bin/day2406.ml

@@ -1,16 +1,4 @@
-(** [IntPair] is a module describing pairs of ints, suitable for using with
-    [Set.Make]. *)
-module IntPair = struct
-  type t = int * int
-
-  let compare (x, y) (x', y') =
-    match compare y y' with 0 -> compare x x' | c -> c
-end
-
-module PosSet = Set.Make (IntPair)
-(** [PosSet] represents a set of positions. *)
-
-type map = { blocks : PosSet.t; width : int; height : int }
+type map = { blocks : Aoc.IntPairSet.t; width : int; height : int }
 (** [map] represents a map with [blocks] and a [width] and [height]. *)
 
 (** [find_start strs] returns the location [(x, y)] of the starting position. *)
@@ -29,14 +17,14 @@ let find_start strs =
 let map_of_strings strs =
   let rec row_scan acc y pos s =
     match String.index_from_opt s pos '#' with
-    | Some x -> row_scan (PosSet.add (x, y) acc) y (x + 1) s
+    | Some x -> row_scan (Aoc.IntPairSet.add (x, y) acc) y (x + 1) s
     | None -> acc
   in
   let rec impl acc y = function
     | h :: t -> impl (row_scan acc y 0 h) (y + 1) t
     | [] -> (acc, y)
   in
-  let blocks, height = impl PosSet.empty 0 strs in
+  let blocks, height = impl Aoc.IntPairSet.empty 0 strs in
   let width = String.length (List.hd strs) in
   { blocks; height; width }
 
@@ -62,7 +50,7 @@ let is_valid_pos map (x, y) =
     the updated [(pos, vel)] pair. *)
 let rec move map ((x, y), (dx, dy)) =
   let x', y' = (x + dx, y + dy) in
-  if PosSet.mem (x', y') map.blocks then move map ((x, y), (-dy, dx))
+  if Aoc.IntPairSet.mem (x', y') map.blocks then move map ((x, y), (-dy, dx))
   else ((x', y'), (dx, dy))
 
 (** [walk_map map (pos, vel)] walks around [map] starting at [pos] moving in the
@@ -97,15 +85,15 @@ let has_cycles map (pos, vel) =
 let walk_block map (pos, vel) bpos =
   if bpos = pos then false
   else
-    let map' = { map with blocks = PosSet.add bpos map.blocks } in
+    let map' = { map with blocks = Aoc.IntPairSet.add bpos map.blocks } in
     has_cycles map' (pos, vel)
 
 let part1 (map, pos, vel) =
-  walk_map map (pos, vel) |> List.sort_uniq IntPair.compare |> List.length
+  walk_map map (pos, vel) |> List.sort_uniq Aoc.IntPair.compare |> List.length
 
 let part2 (map, pos, vel) =
   walk_map map (pos, vel)
-  |> List.sort_uniq IntPair.compare
+  |> List.sort_uniq Aoc.IntPair.compare
   |> List.filter (walk_block map (pos, vel))
   |> List.length