solve day 18!

it was kinda ez

.ocamlformat

@@ -1,2 +1 @@
 profile = janestreet
-version = 0.26.0

.ocamlinit

@@ -1,2 +1,2 @@
 #install_printer Aoc.Vec2.pp;;
-#install_printer Aoc.Vec2.pp_grid;;
+#install_printer Aoc.Grid.pp;;

aoc.opam

@@ -10,11 +10,11 @@ homepage: "https://github.com/username/reponame"
 doc: "https://url/to/documentation"
 bug-reports: "https://github.com/username/reponame/issues"
 depends: [
-  "ocaml"
-  "dune" {>= "3.10"}
   "utop"
   "ocaml-lsp-server"
   "ocamlformat"
+  "ocaml"
+  "dune" {>= "3.10"}
   "re"
   "containers"
   "iter"

inputs/day16.tt

@@ -0,0 +1,60 @@
+Valve XB has flow rate=0; tunnels lead to valves WZ, LE
+Valve BM has flow rate=0; tunnels lead to valves PL, RI
+Valve GC has flow rate=0; tunnels lead to valves HN, IT
+Valve RM has flow rate=0; tunnels lead to valves ZQ, YL
+Valve ZM has flow rate=5; tunnels lead to valves SN, KE, UW, MY, GW
+Valve UH has flow rate=0; tunnels lead to valves HM, HN
+Valve GW has flow rate=0; tunnels lead to valves LE, ZM
+Valve HN has flow rate=19; tunnels lead to valves UW, UH, GL, WZ, GC
+Valve VT has flow rate=0; tunnels lead to valves ZD, PE
+Valve VI has flow rate=0; tunnels lead to valves JS, AA
+Valve YL has flow rate=12; tunnels lead to valves PM, MH, RM, CM
+Valve LA has flow rate=0; tunnels lead to valves SN, IY
+Valve CM has flow rate=0; tunnels lead to valves YL, UL
+Valve JI has flow rate=24; tunnels lead to valves UV, WH, XW, OJ
+Valve ZD has flow rate=25; tunnels lead to valves VB, XW, VT
+Valve VB has flow rate=0; tunnels lead to valves QX, ZD
+Valve FO has flow rate=0; tunnels lead to valves WH, PE
+Valve JS has flow rate=0; tunnels lead to valves VI, IY
+Valve RI has flow rate=0; tunnels lead to valves PE, BM
+Valve XD has flow rate=14; tunnel leads to valve CP
+Valve ES has flow rate=11; tunnels lead to valves GU, WU
+Valve WZ has flow rate=0; tunnels lead to valves XB, HN
+Valve HW has flow rate=0; tunnels lead to valves QY, LE
+Valve KE has flow rate=0; tunnels lead to valves AA, ZM
+Valve IY has flow rate=22; tunnels lead to valves JS, AB, LA, IT
+Valve XW has flow rate=0; tunnels lead to valves ZD, JI
+Valve BE has flow rate=0; tunnels lead to valves AB, LE
+Valve QY has flow rate=23; tunnels lead to valves AM, HW, MY
+Valve MH has flow rate=0; tunnels lead to valves YL, AM
+Valve IT has flow rate=0; tunnels lead to valves GC, IY
+Valve DA has flow rate=0; tunnels lead to valves QR, CP
+Valve PM has flow rate=0; tunnels lead to valves LE, YL
+Valve WU has flow rate=0; tunnels lead to valves SM, ES
+Valve UL has flow rate=0; tunnels lead to valves CM, QR
+Valve SM has flow rate=13; tunnel leads to valve WU
+Valve XC has flow rate=0; tunnels lead to valves ZJ, AA
+Valve OJ has flow rate=0; tunnels lead to valves GI, JI
+Valve SN has flow rate=0; tunnels lead to valves LA, ZM
+Valve WH has flow rate=0; tunnels lead to valves JI, FO
+Valve UW has flow rate=0; tunnels lead to valves HN, ZM
+Valve HM has flow rate=0; tunnels lead to valves UH, PE
+Valve AB has flow rate=0; tunnels lead to valves BE, IY
+Valve QR has flow rate=8; tunnels lead to valves WW, UL, DA
+Valve UV has flow rate=0; tunnels lead to valves JI, FF
+Valve ZQ has flow rate=20; tunnel leads to valve RM
+Valve ZJ has flow rate=0; tunnels lead to valves PE, XC
+Valve GL has flow rate=0; tunnels lead to valves HN, PL
+Valve CP has flow rate=0; tunnels lead to valves DA, XD
+Valve AM has flow rate=0; tunnels lead to valves QY, MH
+Valve PL has flow rate=17; tunnels lead to valves GL, YE, BM, FF, QX
+Valve YE has flow rate=0; tunnels lead to valves PL, AA
+Valve PE has flow rate=4; tunnels lead to valves FO, RI, ZJ, VT, HM
+Valve MY has flow rate=0; tunnels lead to valves QY, ZM
+Valve QX has flow rate=0; tunnels lead to valves VB, PL
+Valve GI has flow rate=0; tunnels lead to valves OJ, AA
+Valve WW has flow rate=0; tunnels lead to valves GU, QR
+Valve FF has flow rate=0; tunnels lead to valves UV, PL
+Valve LE has flow rate=6; tunnels lead to valves HW, GW, XB, BE, PM
+Valve GU has flow rate=0; tunnels lead to valves ES, WW
+Valve AA has flow rate=0; tunnels lead to valves KE, GI, VI, YE, XC

inputs/day17.tt

@@ -0,0 +1 @@
+><<<<>>>><>>><<><<<<>>>><<>>><>>><<<<>>>><<>>>><<<>>>><<<>>>><<<>>><<<<>><>><<<<>>><><<<><><>>>><<<<><<<<>><<<>>>><<>><><>>>><<<>>><<<>>><<>>>><>>>><>><>>><<>><><<<<><>><<<>>>><<<>>><<<>><>><<<>>><<<<>>>><><<<>>><<<>>><<<<><<<<>>><<<<>>><<<>>><<<<>>><<>>><<><<<>><<<>>><<<<><<<<>>><<<><<>>>><<<>><>>><<>>><<<><<<<>>><<><<<<>>>><<>>>><<>>>><<<<>>><><<<<><>><<<>>>><<<<>><>>>><>><>><>><<<>><<<>>>><<<>><<>><<<<><<<<><<>>>><<<<><<<>>><>><<<>>><<<><<<><<<<><<><<<>>><<<<>>>><<<<><<>><<<<>>><>>><<<<><<<>>>><<><>><<<<>><<<<>>>><<<><<<<><<<<>>><<<><<>>><>>><<<<>>><<>><<<<>>><<<><<<>><<<<>>>><<<<><<><<<<>>>><>>>><<<<>>>><<<>>>><<<><<>>><>>><<<<>><<<<>>><><>><<<>>>><<<<>><<<>><<>><<<>>><<<>>>><<<<>>>><<>>>><<>>>><><<<<>><<<<>>>><<<<>>><<<<>><>><<<>>><>>>><><<>><<>>><<<>>>><>>><<>><<<>><>>><>>><><>><>><<<><<<>>>><>><<<><<<>>><<<<><<>>>><<<><<<>>>><>><<<>>>><<<>>>><>>><><>>>><>><<><<<>>>><<>>>><<<>>><<<<>>><<<>><>>>><<<<>>>><>><<>>><<<<>>>><<<<><>>>><<>><<>>>><>><<<<>>>><<<<>><<<>>>><<>><><>><<<<>><<<>>>><<<>>><<>><><<<>>>><<>><>><<>><>><<<<>><<<>>><<<<>>><<>>>><<>>><<<<>>><>><<><<<>><>>><<<>><<<<>>>><<<>>><<>>><<<>>><<<<>>>><<<<>>><<<>>><<>>>><<>>><<<>>><<><<>>>><<>>>><<><<>>><<><<<>>>><<<<><<<<>><<<>>>><>>><<<<>>><<<<>>>><<>><<<<>>>><<<><<<><<>>>><<<>>>><<<>>>><<<>><<>>><>>><<<<>>><<<<>><<<>>><<<>><<<<>>><<<<><<><>>><<<<>>><<<<>>>><>><<<<>><<<<>>>><<<<><<<>>>><>><<<<><<<<>>>><>><<><<<>>><<>>><<<<>><<<><<<><>><<>>>><<<><<<<><<<>>>><<<<>><<>><<<<>>>><><<<><<<>>>><<>>>><<>><<<<>>>><><><<<<><><<>>><<><<>>><>>><<>><><<><<>>>><<<<><<<>>>><<>><><<>>>><<<<><><<<>>>><<>>><<<><<<>>>><>><<<<>>>><>>><<><>>>><>>>><<<><>>><>>>><<<>><<<>>><<<<>>>><<>>>><<<<>>>><<><>><<<<>><<<<>>><<>>><>>>><<><<>>><>>>><<><<><<><><<<>><>><<<<>>><<<>>>><<<><<<<>><>><>>><<<<><<<>>>><<<>>><><<<<>>><<<<><<<<>>>><>><>>><<<><<>><<<><>>><<<<>><><<<<><>><<>><<>><>><<<<><<<>><>>>><<>><<<<>>><><<<>><<>><<>><>>><>>>><<><>><<<<>>><>>><<>>><<>>>><<>><<<<>>><>><<<>>><<<>>><<<<>>>><<<><<<<>><<><<<><<<>>><<><<>><>><>>><<<>>><<>><<>>><<>><<>><>><<<<>>>><<<<>>><<<>>>><<<<>>><<<>><<<>><<<<>>>><<>><<<<><<<<>><<>>><><<><<<<>>>><><>>>><<<<>>>><<<<>>>><<>><<<<>>>><<<><>><<>>>><<>>>><<<<>>>><<<>>><>><<>>>><<<>>>><<<<>>><<<<>><<<<>>>><<>>><<>>>><>>><>>>><><>><<<<>>>><<<>>>><<<>><<>>><<<<>>><>>>><<>>>><<<><>>><><<>>>><<>>>><<<>>>><<<<><<<<>>>><>>>><>><<<>>><<<>>>><<<>><<<>>><>><<>>><<><><<><<>>>><>>><<<<>><><>><>>><<<<><>>><<<>>><<<><<<<>>><<<>><<<>>><<>>><<<<><<<<><>><><<<<>>><<<>><<>><<<>><<<<>><>><>>>><<>>><<<>><<<>><<<<>><><<<<>>><<<>>>><<<<>>><<>><>><<>>><><<>>><<<>>><<<>><<>>>><<<<>><<<<>>>><<<><<><<<<>><<<<>><<<>>>><>><<<><>>>><<>>>><<><<<>>>><<<<>><<<>>>><<>>><>><<<<>>>><<<<>>><>>>><<<<><<><<>><>><>>><<<><<<<><<<<>><<<>>><<<<>><<><<<<>>>><<<>>>><<<>>>><<<<>>><<><<>><<><<<<>>>><<<><<<<>>>><<>>><<<<>><>>>><<<<>><<<>>>><<><<<<>>>><<<>><>>>><><<<>><<<><<<>>><>>>><>>><<<<><<<<>>><<>>><<<>>><<<<><<<<>>>><<>>><<<>><<>>><><<<>>>><<><>>><<>><<<>>>><<<><>><<<>>><<>>>><<<>>>><>><<><>><<>>>><<<>>>><<<<>>>><<<>>><<<>><<<<><<<<>><><<><<<>><>>><<<<>>><<<<>><<<>>><<>><<<<><<<><<<><<<>>><<<<>>><<<<>><<>>><<>><<<<>>>><<>>>><<>>>><<>><>>><>>>><<>>>><<<>>><<<<>>><>>><>>>><<<>><<>>><<>>>><<>>>><<<>>><<>>><<<><<<>><>>>><<<>><>>><<<>>><>>>><>><<>>><<<<>>><<<<>><>>><<<<>>><<<<><<<>>><><>>><<<>>><>><>>>><<>>>><<<>><<>>><<>><<<<>><<<<><>>><<>><<<<>>><<<>>><<>>>><>>>><<<><>>>><<><><>>><<>>>><<<>>>><><>><<<<>><<<>>>><<<<><<<<>>>><<<<>><>>>><<<>>>><<><<>>>><<<<>>>><<<<>>><>><>>>><>>>><>><<>>>><>>>><<>>><<<<>>>><<>>><><<>>>><<>><<<<><<><>>>><<<<>><<><<><<>><<<><<<>><<<<>>><<<<>><<>><>>><<<<>>>><<<<>>>><<<<>>><><<<<><<<<><><<<<><<<<>>>><<<<>>>><><>>><<<<><<<<><<<><><<<<>><><<<><<<<>><>>><><><<<><>>><<><<>><<<>><<<>>>><<<<>>><<>><<<<><>>><>>><<>>>><<<<>>><<<>>>><<<>>>><<<>><<<>><<<<>>><<<<>><>>><<<<><>>>><<<>><>>><<>>><<<<>><<><<<>><>>><<<>><<<<>>><<<>>>><>>><><<<><<<>>>><<>>><<><>>>><>>>><<<<>>><><><>>>><<<<>><<<<>>><<>>><<<><<<>>>><<><<<>><<<>>>><<<<>>>><>>><<<>>><><<<>><<<<>><<<>>>><>><<><><<>><<<>><<<>>><<<<>>>><<<><<<<>><<<<>>>><<<<>>>><<><<<<>>><<<<>><<<<>><<<>><<<<>>><<>>>><<>>><>><<>>>><>>><>>><<<><>>>><<<>>><<<<><<<<>>><<><><>>>><<>>>><<>>>><<<<>>>><<><<><<<>>><<<>>>><<><<<><<>>><<<><<<>>>><<<<>>><<>>>><<>><><<<><<>><<>>><<<<>><>><<<>><<<<>><<<<><<>>><<><<<<>>>><<<>><<<<>><<>>>><>>>><>>><>>>><<<>>><<<>>>><<>>>><>><>><<<>><<<>>><<>>><<<<>>><<<<>>><<>>>><>>><>><<<<>>>><<>>>><<>>>><<<<>>>><>>>><><>>><<>>>><<<<><<>>>><<<<>><<<<>>>><<>><<<<><<<<>>><<<<>><<>>>><<<>>>><<<><>><<<><<>>><<<<>><<<>>><><<<<>><<<<>><>>><<<<>>><<<<>>>><>>>><<>>>><<>>><>>>><<<<>>><<>><<<><<><<<>>>><<<>>>><<<<><<>>><>><<<<><<<>>><>><><<<><<>>>><>>>><>><<>>><<>>>><<>>>><<<<>><<>><><<>>><<>><<>><<>>><>><<<<>>>><<>>>><<<<>>><<>><><<<><>><<<>><>>><>><<>>><><>>><<>>>><<<>>><<<<>>><<<>><<>><<<<>>><<<><<<>><<<<><<>><>><<<<>><<>>>><<<>><<<>>>><<<<>>>><<<<>><<>>><<<>>><<<>>>><<<<>>><<<<>>>><>><<<<>>>><<>>><><<>>>><<<<>>>><<<<>>>><>><<>><<<<><<<<>>><><>>><<<<>>><<><>>>><<<<><<<>>>><>>>><<<>>>><<<>>>><<>>><<>>><<<<><<<>><>>><<<><<<>>><Line truncated

src/day12.ml

@@ -1,7 +1,5 @@
 open Containers
 
-let infinity = 1000000000
-
 type node =
   { char : char
   ; mutable visited : bool
@@ -10,25 +8,20 @@ type node =
 [@@deriving show]
 
 let parse_grid start_anywhere =
-  let s = ref @@ Vec2.origin in
-  let e = ref @@ Vec2.origin in
-  let unvisited = ref [] in
+  let start_nodes = ref [] in
+  let end_node = ref @@ Vec2.origin in
   let grid =
     Utils.lines_of_input 12
-    |> Grid.of_lines (fun char -> { char; visited = false; distance = infinity })
+    |> Grid.of_lines (fun char -> { char; visited = false; distance = Int.max_int })
   in
   Grid.iter grid (fun pos ->
-    let n = Grid.at_e grid pos in
-    match n.char with
-    | 'E' -> e := pos
-    | 'S' ->
-      n.distance <- 0;
-      s := pos
-    | 'a' when start_anywhere ->
-      n.distance <- 0;
-      unvisited := pos :: !unvisited
+    let node = Grid.at_e grid pos in
+    match node.char with
+    | 'E' -> end_node := pos
+    | 'S' -> start_nodes := pos :: !start_nodes
+    | 'a' when start_anywhere -> start_nodes := pos :: !start_nodes
     | _ -> ());
-  grid, !e, !s, !unvisited
+  grid, !end_node, !start_nodes
 ;;
 
 let reachable f t =
@@ -41,42 +34,67 @@ let reachable f t =
   Char.compare (height f) (height t) >= -1
 ;;
 
-let rec path grid goal current unvisited =
-  let current_node = Grid.at_e grid current in
+let get_neighbors grid node_pos =
+  let node = Grid.at_e grid node_pos in
   Vec2.directions
-  |> List.map (fun dir -> Vec2.(current + dir))
-  |> List.iter (fun neighbor ->
-    match Grid.at grid neighbor with
-    | Some node when (not node.visited) && reachable current_node.char node.char ->
-      let new_distance = current_node.distance + 1 in
-      if new_distance < node.distance then node.distance <- new_distance;
-      if Option.is_none @@ List.find_opt (fun x -> Vec2.(x = neighbor)) !unvisited
-      then unvisited := neighbor :: !unvisited
-    | _ -> ());
-  current_node.visited <- true;
-  unvisited
-    := List.sort
-         (fun a b ->
-           let a = Grid.at_e grid a in
-           let b = Grid.at_e grid b in
-           a.distance - b.distance)
-         !unvisited;
-  match !unvisited with
-  | shortest :: _ when Vec2.(shortest = goal) -> Grid.at grid shortest
-  | shortest :: rest -> path grid goal shortest @@ ref rest
-  | [] -> None
+  |> Iter.of_list
+  |> Iter.filter_map (fun dir ->
+    let neighbor_pos = Vec2.(node_pos + dir) in
+    match Grid.at grid neighbor_pos with
+    | Some neighbor when reachable node.char neighbor.char -> Some neighbor_pos
+    | _ -> None)
+;;
+
+let path_distance grid goal start_nodes =
+  let set_info position (dist, visited) =
+    let node = Grid.at_e grid position in
+    node.distance <- dist;
+    node.visited <- visited
+  in
+  let get_info position =
+    let { char = _; distance; visited } = Grid.at_e grid position in
+    distance, visited
+  in
+  Utils.djikstra
+    ~set_info
+    ~get_info
+    ~eq:Vec2.( = )
+    ~get_weight:(fun _ _ -> 1)
+    ~get_neighbors:(get_neighbors grid)
+    ~goal
+    ~start_nodes
+  |> Option.get_exn_or "couldn't find"
 ;;
 
 let%expect_test "Day 12.1" =
-  let grid, e, s, unvisited = parse_grid false in
-  let solution = Option.get_exn_or "coulnd't find" @@ path grid e s @@ ref unvisited in
-  Printf.printf "%d" solution.distance;
+  let grid, goal, start_nodes = parse_grid false in
+  Printf.printf "%i" @@ path_distance grid (Some goal) start_nodes;
   [%expect {| 497 |}]
 ;;
 
 let%expect_test "Day 12.2" =
-  let grid, e, s, unvisited = parse_grid true in
-  let solution = Option.get_exn_or "coulnd't find" @@ path grid e s @@ ref unvisited in
-  Printf.printf "%d" solution.distance;
+  let grid, goal, start_nodes = parse_grid true in
+  Printf.printf "%i" @@ path_distance grid (Some goal) start_nodes;
   [%expect {| 492 |}]
 ;;
+
+let%expect_test "Day 12 test" =
+  let grid, goal, start_nodes = parse_grid false in
+  let _ = path_distance grid None start_nodes in
+  let print_dist_to pos =
+    let node = Option.get_exn_or "invalid pos!" grid.Grid.%(pos) in
+    Printf.printf "%s %c %i\n" (Vec2.show pos) node.char node.distance
+  in
+  print_dist_to goal;
+  print_dist_to Vec2.(goal + right);
+  print_dist_to Vec2.(goal + down);
+  print_dist_to Vec2.(of_tuple (121, 23));
+  print_dist_to Vec2.(origin + right);
+  [%expect
+    {|
+    (149, 20) E 497
+    (150, 20) z 498
+    (149, 21) y 496
+    (121, 23) a 138
+    (1, 0) b 21 |}]
+;;

src/day14.ml

@@ -9,7 +9,7 @@ type tile =
   | Path_L
   | Path_R
 
-let char_of_tile = function
+let char_of_tile _ = function
   | Empty -> '-'
   | Rock -> '#'
   | Sand -> 'o'
@@ -43,9 +43,9 @@ let draw_rocks grid points =
 ;;
 
 let parse_grid lines start =
-  let points = List.map parse_line lines in
+  let points = Iter.map Fun.(parse_line %> Iter.of_list) lines in
   let Vec2.{ x = lx; y = ly }, Vec2.{ x = hx; y = hy } =
-    points |> List.flatten |> List.append [ start ] |> Vec2.bounds 0
+    points |> Iter.flatten |> Iter.cons start |> Vec2.find_bounds 0
   in
   let pad_floor = 1 in
   let pad_x = 2 in
@@ -58,8 +58,9 @@ let parse_grid lines start =
   let open Grid in
   let grid = init ~width ~height (fun _ -> Empty) in
   grid.%(start) <- Start;
-  points
-  |> List.iter Fun.(List.map (fun point -> Vec2.(point - extra)) %> draw_rocks grid);
+  Iter.iter
+    Fun.(Iter.map (fun point -> Vec2.(point - extra)) %> Iter.to_list %> draw_rocks grid)
+    points;
   grid, start
 ;;
 
@@ -118,7 +119,9 @@ let rec drop_all_sand drop grid start =
 ;;
 
 let%expect_test "Day 14.1 example" =
-  let lines = [ "498,4 -> 498,6 -> 496,6"; "503,4 -> 502,4 -> 502,9 -> 494,9" ] in
+  let lines =
+    Iter.of_list [ "498,4 -> 498,6 -> 496,6"; "503,4 -> 502,4 -> 502,9 -> 494,9" ]
+  in
   let start = Vec2.of_tuple (500, 0) in
   let grid, start = parse_grid lines start in
   drop_all_sand (drop_sand_abyss false) grid start;
@@ -142,7 +145,9 @@ let%expect_test "Day 14.1 example" =
 ;;
 
 let%expect_test "Day 14.2 example" =
-  let lines = [ "498,4 -> 498,6 -> 496,6"; "503,4 -> 502,4 -> 502,9 -> 494,9" ] in
+  let lines =
+    Iter.of_list [ "498,4 -> 498,6 -> 496,6"; "503,4 -> 502,4 -> 502,9 -> 494,9" ]
+  in
   let start = Vec2.of_tuple (500, 0) in
   let grid, start = parse_grid lines start in
   drop_all_sand drop_sand_floor grid start;
@@ -165,7 +170,7 @@ let%expect_test "Day 14.2 example" =
 ;;
 
 let%expect_test "Day 14.1" =
-  let lines = Utils.lines_of_input 14 in
+  let lines = Iter.of_list @@ Utils.lines_of_input 14 in
   let start = Vec2.of_tuple (500, 0) in
   let grid, start = parse_grid lines start in
   drop_all_sand (drop_sand_abyss false) grid start;
@@ -175,7 +180,7 @@ let%expect_test "Day 14.1" =
 ;;
 
 let%expect_test "Day 14.2" =
-  let lines = Utils.lines_of_input 14 in
+  let lines = Iter.of_list @@ Utils.lines_of_input 14 in
   let start = Vec2.of_tuple (500, 0) in
   let grid, start = parse_grid lines start in
   drop_all_sand drop_sand_floor grid start;

src/day15.ml

@@ -1,31 +1,5 @@
 open Containers
 
-type sensor =
-  { pos : Vec2.t
-  ; beacon : Vec2.t
-  ; dist : int
-  }
-[@@deriving show { with_path = false }]
-
-let taxicab_dist a b =
-  let x, y = Vec2.(abs (a - b) |> to_tuple) in
-  x + y
-;;
-
-let parse_sensor line =
-  let open Utils.Parse in
-  let parse =
-    many1 (not_int *> int)
-    >>= function
-    | [ sx; sy; bx; by ] ->
-      let pos = Vec2.of_tuple (sx, sy) in
-      let beacon = Vec2.of_tuple (bx, by) in
-      return { pos; beacon; dist = taxicab_dist pos beacon }
-    | _ -> failwith "should be four ints"
-  in
-  Result.get_or_failwith @@ parse_string ~consume:All parse line
-;;
-
 let example_lines =
   [ "Sensor at x=2, y=18: closest beacon is at x=-2, y=15"
   ; "Sensor at x=9, y=16: closest beacon is at x=10, y=16"
@@ -44,17 +18,29 @@ let example_lines =
   ]
 ;;
 
-let bounds sensors =
-  let max_dist = sensors |> List.fold_left (fun acc s -> max acc s.dist) 0 in
-  sensors
-  |> List.flat_map (fun sensor -> [ sensor.pos; sensor.beacon ])
-  |> Vec2.bounds max_dist
+type sensor =
+  { pos : Vec2.t
+  ; beacon : Vec2.t
+  ; dist : int
+  }
+[@@deriving show { with_path = false }]
+
+let taxicab_dist a b =
+  let x, y = Vec2.(abs (a - b) |> to_tuple) in
+  x + y
+;;
+
+let parse_sensor line =
+  match List.map int_of_string Re.(matches (Pcre.regexp {|-?\d+|}) line) with
+  | [ sx; sy; bx; by ] ->
+    let pos, beacon = Vec2.(of_tuple (sx, sy), of_tuple (bx, by)) in
+    { pos; beacon; dist = taxicab_dist pos beacon }
+  | _ -> failwith "parse error"
 ;;
 
 let could_be_beacon sensors ignore_known pos =
-  let open Iter in
-  of_list sensors
-  |> fold_while
+  sensors
+  |> Iter.fold_while
        (fun _ s ->
          let d = taxicab_dist pos s.pos in
          if d <= s.dist && (ignore_known || not Vec2.(pos = s.beacon))
@@ -63,95 +49,102 @@ let could_be_beacon sensors ignore_known pos =
        true
 ;;
 
-(* let%expect_test "Day 15.1" = *)
-(*   let sensors = Utils.lines_of_input 15 |> List.map parse_sensor in *)
-(*   let scan_row = 2000000 in *)
-(*   let Vec2.{ x = lx; _ }, Vec2.{ x = hx; _ } = bounds sensors in *)
-(*   Vec2.fold_region *)
-(*     Vec2.{ x = lx; y = scan_row } *)
-(*     Vec2.{ x = hx; y = scan_row } *)
-(*     (fun acc pos -> if could_be_beacon sensors false pos then acc else acc + 1) *)
-(*     0 *)
-(*   |> Printf.printf "%i\n"; *)
-(*   [%expect {| 5525990 |}] *)
-(* ;; *)
+(*{[
+    equation for line
+      y = m*x + c
 
-(* module VecTbl = Hashtbl.Make (Vec2) *)
+    beacon range boundaries are made up of four lines:
+      slope  1 passing thru bx + dist + 1, by
+      slope  1 passing thru bx - dist - 1, by
+      slope -1 passing thru bx + dist + 1, by
+      slope -1 passing thru bx - dist - 1, by
 
-(* let points_on_border tbl sensor = *)
-(*   let points = ref [] in *)
-(*   let dist = sensor.dist + 1 in *)
-(*   for d1 = 0 to dist do *)
-(*     let d2 = dist - d1 in *)
-(*     let open Vec2 in *)
-(*     let p1 = of_tuple (d1, d2) in *)
-(*     let p2 = of_tuple (d1, Int.(-d2)) in *)
-(*     let new_points = *)
-(*       [ sensor.pos + p1; sensor.pos - p1; sensor.pos + p2; sensor.pos - p2 ] *)
-(*       |> List.fold_left *)
-(*            (fun acc point -> *)
-(*              match VecTbl.find_opt tbl point with *)
-(*              | Some false -> acc *)
-(*              | Some true -> *)
-(*                VecTbl.replace tbl point false; *)
-(*                point :: acc *)
-(*              | None -> *)
-(*                VecTbl.add tbl point true; *)
-(*                acc) *)
-(*            [] *)
-(*     in *)
-(*     points := !points @ new_points *)
-(*   done; *)
-(*   !points *)
-(* ;; *)
+    to find the constant given a slope, plug a point into
+      c = y - m*x
 
-(* let%expect_test "Day 15.2 brute force" = *)
-(*   let sensors = Utils.lines_of_input 15 |> List.map parse_sensor in *)
-(*   let mult = 4000000 in *)
-(*   let range = mult in *)
-(*   let in_bounds = Vec2.(in_bounds origin @@ of_tuple (range, range)) in *)
-(*   let tbl = VecTbl.create (range * 10) in *)
-(*   let point = *)
-(*     sensors *)
-(*     |> Iter.of_list *)
-(*     |> Iter.flat_map_l @@ points_on_border tbl *)
-(*     |> Iter.fold_while *)
-(*          (fun _ v -> *)
-(*            if in_bounds v && could_be_beacon sensors true v *)
-(*            then Some v, `Stop *)
-(*            else None, `Continue) *)
-(*          None *)
-(*     |> Option.get_exn_or "fucc :(" *)
-(*   in *)
-(*   Printf.printf "%i\n" ((mult * point.x) + point.y); *)
-(*   [%expect {| 11756174628223 |}] *)
-(* ;; *)
+    constants are stored separately for boundaries with positive and negative
+    slope so that they can be handled separately
+      p1 = y - bx - dist - 1
+      p2 = y - bx + dist + 1
+      n1 = y + bx + dist + 1
+      n2 = y + bx - dist - 1
+  ]}*)
+let get_consts sensors extra =
+  sensors
+  |> Iter.fold
+       (fun (p_slope_consts, n_slope_consts) { pos; beacon = _; dist } ->
+         let p1 = pos.y - pos.x + dist + extra in
+         let p2 = pos.y - pos.x - dist - extra in
+         let n1 = pos.y + pos.x + dist + extra in
+         let n2 = pos.y + pos.x - dist - extra in
+         Iter.(
+           ( append p_slope_consts (of_list [ p1; p2 ])
+           , append n_slope_consts (of_list [ n1; n2 ]) )))
+       (Iter.empty, Iter.empty)
+;;
 
-module IntSet = Set.Make (Int)
+let solve_part_1 lines scan_y =
+  let sensors = lines |> Iter.of_list |> Iter.map parse_sensor in
+  let p_slope_consts, n_slope_consts = get_consts sensors 0 in
+  (*{[
+      for a known y to intersect with a positive slope boundary:
+        y = x + p
+        x = y - p
 
-let%expect_test "Day 15.2" =
-  let sensors = Utils.lines_of_input 15 |> List.map parse_sensor in
-  let mult = 4000000 in
-  let range = mult in
-  let in_bounds = Vec2.(in_bounds origin @@ of_tuple (range, range)) in
-  let pos_coeffs, neg_coeffs =
-    sensors
-    |> Iter.of_list
-    |> Iter.fold
-         (fun (pos_coeffs, neg_coeffs) { pos; beacon = _; dist } ->
-           let p1 = pos.y - pos.x + dist + 1 in
-           let p2 = pos.y - pos.x - dist - 1 in
-           let n1 = pos.y + pos.x + dist + 1 in
-           let n2 = pos.y + pos.x - dist - 1 in
-           Iter.(
-             ( append pos_coeffs (of_list [ p1; p2 ])
-             , append neg_coeffs (of_list [ n1; n2 ]) )))
-         (Iter.empty, Iter.empty)
+      and for a negative slope boundary:
+        y = -x + n
+        x = n - y
+    ]}*)
+  let intersection_xs =
+    Iter.append
+      (Iter.map (fun p -> scan_y - p) p_slope_consts)
+      (Iter.map (fun n -> n - scan_y) n_slope_consts)
+    |> Iter.sort_uniq ~cmp:Int.compare
   in
+  let check x = could_be_beacon sensors false @@ Vec2.of_tuple (x, scan_y) in
+  let rec count_not_beacons count xs =
+    match xs with
+    | x :: next :: rest ->
+      (* if there is a region [x+1, next), the value of check
+         is the same for each point within it. intersection points
+         must be checked separately from the regions between them  *)
+      let intersection = if check x then 0 else 1 in
+      let region = if x + 1 < next && check (x + 1) then 0 else next - (x + 1) in
+      count_not_beacons (count + intersection + region) (next :: rest)
+    | _ -> count
+  in
+  count_not_beacons 0 @@ Iter.to_list intersection_xs
+;;
+
+let%expect_test "Day 15.1 example" =
+  Printf.printf "%i\n" @@ solve_part_1 example_lines 10;
+  [%expect {| 26 |}]
+;;
+
+let%expect_test "Day 15.1" =
+  Printf.printf "%i\n" @@ solve_part_1 (Utils.lines_of_input 15) 2000000;
+  [%expect {| 5525990 |}]
+;;
+
+let solve_part_2 lines range mult =
+  let sensors = lines |> Iter.of_list |> Iter.map parse_sensor in
+  let in_bounds = Vec2.(in_bounds origin @@ of_tuple (range, range)) in
+  let p_slope_consts, n_slope_consts = get_consts sensors 1 in
+  (*{[
+      boundaries only itersect if they have opposite slope.
+      to find the intersection, set equations to be equal and solve.
+         y =  x + p
+         y = -x + n        // set equal
+         x + p = -x + n    // add x and subtract p
+         2x = n - p        // divide 2
+      -> x = (n - p)/2     // substitute x into original
+         y = (n - p)/2 + p // multiply 2
+         2y = n + p        // div 2
+      -> y = (n + p)/2
+    ]}*)
   let point =
-    let open Iter in
-    product pos_coeffs neg_coeffs
-    |> fold_while
+    Iter.product p_slope_consts n_slope_consts
+    |> Iter.fold_while
          (fun _ (p, n) ->
            let i = Vec2.of_tuple ((n - p) / 2, (n + p) / 2) in
            if in_bounds i && could_be_beacon sensors true i
@@ -160,6 +153,15 @@ let%expect_test "Day 15.2" =
          None
     |> Option.get_exn_or "no distress beacon found :("
   in
-  Printf.printf "%i\n" ((mult * point.x) + point.y);
+  (mult * point.x) + point.y
+;;
+
+let%expect_test "Day 15.2 example" =
+  Printf.printf "%i\n" @@ solve_part_2 example_lines 20 4000000;
+  [%expect {| 56000011 |}]
+;;
+
+let%expect_test "Day 15.2" =
+  Printf.printf "%i\n" @@ solve_part_2 (Utils.lines_of_input 15) 4000000 4000000;
   [%expect {| 11756174628223 |}]
 ;;

src/day16.ml

@@ -0,0 +1,141 @@
+open Containers
+
+let example_lines =
+  String.lines
+    {|Valve AA has flow rate=0; tunnels lead to valves DD, II, BB
+Valve BB has flow rate=13; tunnels lead to valves CC, AA
+Valve CC has flow rate=2; tunnels lead to valves DD, BB
+Valve DD has flow rate=20; tunnels lead to valves CC, AA, EE
+Valve EE has flow rate=3; tunnels lead to valves FF, DD
+Valve FF has flow rate=0; tunnels lead to valves EE, GG
+Valve GG has flow rate=0; tunnels lead to valves FF, HH
+Valve HH has flow rate=22; tunnel leads to valve GG
+Valve II has flow rate=0; tunnels lead to valves AA, JJ
+Valve JJ has flow rate=21; tunnel leads to valve II
+|}
+;;
+
+type valve =
+  { flow : int
+  ; mask : int
+  }
+
+let parse_valves lines =
+  let rooms = Hashtbl.create 100 in
+  lines
+  |> List.iter (fun line ->
+    let int_matches = List.map int_of_string Re.(matches (Pcre.regexp {|\d+|}) line) in
+    let valve_matches = Re.(matches (Pcre.regexp {|[A-Z]{2}|}) line) in
+    match int_matches, valve_matches with
+    | [ flow ], name :: tunnels -> Hashtbl.add rooms name (flow, tunnels)
+    | _ -> failwith "parse error");
+  let valves =
+    Hashtbl.to_list rooms
+    |> List.filter (fun (_, (flow, _)) -> flow > 0)
+    |> List.mapi (fun i (name, (flow, _)) ->
+      let mask = Int.(1 lsl i) in
+      name, { flow; mask })
+  in
+  let distances = Hashtbl.create 100 in
+  valves
+  |> List.map (fun (valve, _) -> valve)
+  |> List.cons "AA"
+  |> List.iter (fun from ->
+    let dist_of =
+      Fun.(
+        Utils.djikstra_hash
+          ~get_weight:(fun _ _ -> 1)
+          ~get_neighbors:(fun room ->
+            match Hashtbl.get rooms room with
+            | Some (_, tunnels) -> Iter.of_list tunnels
+            | None -> failwith "sad")
+          ~start_nodes:[ from ]
+          ()
+        %> Option.get_exn_or "big sad")
+    in
+    valves
+    |> List.remove_assoc ~eq:String.equal from
+    |> List.iter (fun (valve, _) ->
+      Hashtbl.replace distances (from, valve) (dist_of valve)));
+  let get_dist f t =
+    match Hashtbl.get distances (f, t) with
+    | Some dist -> dist
+    | None -> failwith @@ Printf.sprintf "cant find distance %s -> %s" f t
+  in
+  valves, get_dist
+;;
+
+let traverse
+  get_dist
+  (valves : (string * valve) list)
+  ?(current = "AA")
+  ?(released = 0)
+  ?(opened = 0)
+  time
+  =
+  let states = Hashtbl.create 1000 in
+  let rec traverse' current time released opened =
+    Hashtbl.update
+      states
+      ~f:(fun _ current ->
+        match current with
+        | Some r when r >= released -> Some r
+        | _ -> Some released)
+      ~k:opened;
+    valves
+    |> List.iter (fun (name, { flow; mask }) ->
+      if Int.(mask land opened) = 0
+      then (
+        let dist = get_dist current name in
+        let time' = time - (dist + 1) in
+        if time' > 0
+        then (
+          let released' = released + (flow * time') in
+          let opened' = Int.(mask lor opened) in
+          traverse' name time' released' opened')))
+  in
+  traverse' current time released opened;
+  states
+  |> Iter.of_hashtbl
+  |> Iter.sort ~cmp:(fun (_, a_score) (_, b_score) -> b_score - a_score)
+;;
+
+let solve_part_1 lines =
+  let valves, get_dist = parse_valves lines in
+  let states = traverse get_dist valves 30 in
+  match states |> Iter.take 1 |> Iter.to_list with
+  | [ (_, score) ] -> score
+  | _ -> failwith "no traversals ?"
+;;
+
+let%expect_test "Day 16.1 example" =
+  Printf.printf "%i\n" @@ solve_part_1 example_lines;
+  [%expect {| 1651 |}]
+;;
+
+let%expect_test "Day 16.1" =
+  Printf.printf "%i\n" @@ solve_part_1 @@ Utils.lines_of_input 16;
+  [%expect {| 2265 |}]
+;;
+
+let solve_part_2 lines =
+  let valves, get_dist = parse_valves @@ lines in
+  let states = traverse get_dist valves 26 in
+  states
+  |> Iter.filter_map (fun (a_set, a_score) ->
+    match Iter.find_pred (fun (b_set, _) -> Int.(a_set land b_set) = 0) states with
+    | Some (_, b_score) -> Some (a_score + b_score)
+    | None -> None)
+  |> Iter.fold Int.max 0
+;;
+
+let%expect_test "Day 16.2 example" =
+  Printf.printf "%i\n" @@ solve_part_2 example_lines;
+  [%expect {| 1707 |}]
+;;
+
+(* god damn bitmasks are fast, 30x speedup from StrSet! down to 50ms now *)
+let%expect_test "Day 16.2" =
+  Printf.printf "%i\n" @@ solve_part_2 @@ Utils.lines_of_input 16;
+  [%expect {| 2811 |}]
+;;

src/day17.ml

@@ -0,0 +1,201 @@
+open Containers
+
+let cave_width = 7
+let example_lines = [ ">>><<><>><<<>><>>><<<>>><<<><<<>><>><<>>" ]
+
+let dir_of_char = function
+  | '<' -> Vec2.left
+  | '>' -> Vec2.right
+  | _ -> failwith "oof"
+;;
+
+let next_stream_idx stream idx = (idx + 1) mod Array.length stream
+
+(*[{
+                       #
+         #       #     #
+        ###      #     #     ##
+ ####    #     ###     #     ##
+
+ row    plus   angle   col   square
+
+}]*)
+type shape =
+  | Row
+  | Plus
+  | Angle
+  | Col
+  | Square
+
+let get_shape idx = [| Row; Plus; Angle; Col; Square |].(idx mod 5)
+
+let shape_points shape pos =
+  let points =
+    match shape with
+    | Row -> [ 0, 0; 1, 0; 2, 0; 3, 0 ]
+    | Plus -> [ 0, 1; 1, 0; 1, 1; 1, 2; 2, 1 ]
+    | Angle -> [ 0, 0; 1, 0; 2, 0; 2, 1; 2, 2 ]
+    | Col -> [ 0, 0; 0, 1; 0, 2; 0, 3 ]
+    | Square -> [ 0, 0; 1, 0; 0, 1; 1, 1 ]
+  in
+  points |> List.map (fun point -> Vec2.(pos + of_tuple point))
+;;
+
+type loop_key =
+  { rock : shape
+  ; stream_idx : int
+  ; normalized_topo : int array
+  }
+
+type loop =
+  { rock_idx : int
+  ; height : int
+  }
+
+type cave =
+  { grid : char Grid.t
+  ; mutable grid_topo : int array
+  ; mutable grid_height : int
+  ; total_rocks : int
+  ; mutable rocks : int
+  ; mutable stream_idx : int
+  ; loop_cache : (loop_key, loop) Hashtbl.t
+  ; mutable height : int
+  }
+
+let init_cave max_height total_rocks =
+  let grid = Grid.init ~width:7 ~height:max_height (Fun.const '.') in
+  { grid
+  ; height = -1
+  ; grid_height = -1
+  ; rocks = 0
+  ; stream_idx = 0
+  ; grid_topo = Array.init cave_width (Fun.const 0)
+  ; loop_cache = Hashtbl.create max_height
+  ; total_rocks
+  }
+;;
+
+let draw_cave cave = Grid.draw cave.grid ~rev_y:true (fun _ contents -> contents)
+
+let place_shape cave shape pos =
+  shape_points shape pos
+  |> List.iter (fun point ->
+    let delta = point.Vec2.y - cave.grid_height in
+    if delta > 0
+    then (
+      cave.height <- cave.height + delta;
+      cave.grid_height <- cave.grid_height + delta);
+    cave.grid_topo.(point.x) <- max point.y cave.grid_topo.(point.x);
+    Grid.set_e cave.grid point '#')
+;;
+
+let can_place_shape cave shape pos =
+  shape_points shape pos
+  |> List.fold_while
+       (fun _ point ->
+         match cave.grid.Grid.%(point) with
+         | Some '.' -> true, `Continue
+         | _ -> false, `Stop)
+       false
+;;
+
+let drop_shape cave stream =
+  let shape = get_shape cave.rocks in
+  let rec drop pos =
+    let stream_pos = Vec2.(pos + stream.(cave.stream_idx)) in
+    cave.stream_idx <- next_stream_idx stream cave.stream_idx;
+    let pos = if can_place_shape cave shape stream_pos then stream_pos else pos in
+    let drop_pos = Vec2.(pos + Vec2.up) in
+    if can_place_shape cave shape drop_pos
+    then drop drop_pos
+    else place_shape cave shape pos
+  in
+  cave.rocks <- cave.rocks + 1;
+  drop Vec2.{ x = 2; y = Int.(cave.grid_height + 4) }
+;;
+
+let normalize_topo topo =
+  let min = Array.min_exn Int.compare topo in
+  Array.map (fun x -> x - min) topo
+;;
+
+let rec drop_shapes cave stream =
+  let loop_key =
+    { rock = get_shape cave.rocks
+    ; stream_idx = cave.stream_idx
+    ; normalized_topo = normalize_topo cave.grid_topo
+    }
+  in
+  let remaining_rocks cave = cave.total_rocks - cave.rocks in
+  let loop_rocks loop = cave.rocks - loop.rock_idx in
+  let loop_fits loop = loop_rocks loop < remaining_rocks cave in
+  match Hashtbl.get cave.loop_cache loop_key with
+  | Some loop when loop_fits loop ->
+    let loop_height = cave.height - loop.height in
+    cave.height <- cave.height + loop_height;
+    cave.rocks <- cave.rocks + loop_rocks loop;
+    drop_shapes cave stream
+  | _ when remaining_rocks cave > 0 ->
+    let loop = { height = cave.height; rock_idx = cave.rocks } in
+    Hashtbl.add cave.loop_cache loop_key loop;
+    drop_shape cave stream;
+    drop_shapes cave stream
+  | _ -> ()
+;;
+
+let solve remaining_rocks lines =
+  let stream = lines |> List.hd |> Iter.of_str |> Iter.map dir_of_char |> Iter.to_array in
+  let cave = init_cave 100_000 remaining_rocks in
+  drop_shapes cave stream;
+  cave.height + 1
+;;
+
+let%expect_test "Day 17.1 Example" =
+  Printf.printf "height: %i\n" @@ solve 2022 example_lines;
+  [%expect {| height: 3068 |}]
+;;
+
+let%expect_test "Day 17.1" =
+  Printf.printf "height: %i\n" @@ solve 2022 (Utils.lines_of_input 17);
+  [%expect {| height: 3227 |}]
+;;
+
+let%expect_test "Day 17.2 Example" =
+  Printf.printf "height: %i\n" @@ solve 1_000_000_000_000 example_lines;
+  [%expect {| height: 1514285714288 |}]
+;;
+
+let%expect_test "Day 17.2" =
+  Printf.printf "height: %i\n" @@ solve 1_000_000_000_000 (Utils.lines_of_input 17);
+  [%expect {| height: 1597714285698 |}]
+;;
+
+let%expect_test "Smol tower" =
+  let stream =
+    example_lines |> List.hd |> Iter.of_str |> Iter.map dir_of_char |> Iter.to_array
+  in
+  let cave = init_cave 18 8 in
+  drop_shapes cave stream;
+  Printf.printf "%s" @@ draw_cave cave;
+  [%expect
+    {|
+    .......
+    .......
+    .......
+    .....#.
+    .....#.
+    ..####.
+    .###...
+    ..#....
+    .####..
+    ....##.
+    ....##.
+    ....#..
+    ..#.#..
+    ..#.#..
+    #####..
+    ..###..
+    ...#...
+    ..####. |}]
+;;

src/day18.ml

@@ -0,0 +1,121 @@
+open Containers
+
+let example_lines =
+  String.lines
+    {|2,2,2
+1,2,2
+3,2,2
+2,1,2
+2,3,2
+2,2,1
+2,2,3
+2,2,4
+2,2,6
+1,2,5
+3,2,5
+2,1,5
+2,3,5|}
+;;
+
+module Vec3 = struct
+  type t = int * int * int [@@deriving show, eq, ord, hash]
+
+  let directions = [ 1, 0, 0; -1, 0, 0; 0, 1, 0; 0, -1, 0; 0, 0, 1; 0, 0, -1 ]
+  let ( + ) (x1, y1, z1) (x2, y2, z2) = x1 + x2, y1 + y2, z1 + z2
+  let ( - ) (x1, y1, z1) (x2, y2, z2) = x1 - x2, y1 - y2, z1 - z2
+  let ( = ) = equal
+
+  let iter_region (ax, ay, az) (bx, by, bz) callback =
+    for z = az to bz do
+      for y = ay to by do
+        for x = ax to bx do
+          let p = x, y, z in
+          callback p
+        done
+      done
+    done
+  ;;
+
+  let in_bounds (lx, ly, lz) (hx, hy, hz) (x, y, z) =
+    not (x < lx || x > hx || y < ly || y > hy || z < lz || z > hz)
+  ;;
+
+  let find_bounds points =
+    let first = Iter.head_exn points in
+    let padding = 1, 1, 1 in
+    let min, max =
+      points
+      |> Iter.drop 1
+      |> Iter.fold
+           (fun ((lx, ly, lz), (hx, hy, hz)) (x, y, z) ->
+             (min lx x, min ly y, min lz z), (max hx x, max hy y, max hz z))
+           (first, first)
+    in
+    min - padding, max + padding
+  ;;
+end
+
+module Vec3Set = Set.Make (Vec3)
+
+let parse_points lines =
+  lines
+  |> List.map (fun line ->
+    match List.map Int.of_string_exn Re.(matches (Pcre.regexp {|\d+|}) line) with
+    | [ x; y; z ] -> x, y, z
+    | _ -> failwith "oopzi doopers")
+  |> Vec3Set.of_list
+;;
+
+let solve_part_1 lines =
+  let points = parse_points lines in
+  let min, max = Vec3.find_bounds @@ Vec3Set.to_iter points in
+  let surface_area = ref 0 in
+  Vec3.iter_region min max (fun point ->
+    if not @@ Vec3Set.mem point points
+    then
+      Vec3.directions
+      |> List.iter (fun dir ->
+        let n = Vec3.(point + dir) in
+        if Vec3Set.mem n points then incr surface_area));
+  !surface_area
+;;
+
+let%expect_test "Day 18.1 example" =
+  Format.printf "%i" @@ solve_part_1 example_lines;
+  [%expect {| 64 |}]
+;;
+
+let%expect_test "Day 18.1" =
+  Format.printf "%i" @@ solve_part_1 @@ Utils.lines_of_input 18;
+  [%expect {| 3662 |}]
+;;
+
+let solve_part_2 lines =
+  let points = parse_points lines in
+  let min, max = Vec3.find_bounds @@ Vec3Set.to_iter points in
+  let in_bounds = Vec3.in_bounds min max in
+  let surface_area = ref 0 in
+  let directions_iter = Iter.of_list Vec3.directions in
+  let get_neighbors point =
+    directions_iter
+    |> Iter.map Vec3.(fun dir -> point + dir)
+    |> Iter.filter (fun neighbor ->
+      let in_droplet = Vec3Set.mem neighbor points in
+      if in_droplet then incr surface_area;
+      (not in_droplet) && in_bounds neighbor)
+  in
+  let _ignore =
+    Utils.djikstra_hash ~get_weight:(fun _ _ -> 1) ~get_neighbors ~start_nodes:[ min ] ()
+  in
+  !surface_area
+;;
+
+let%expect_test "Day 18.2 example" =
+  Format.printf "%i" @@ solve_part_2 example_lines;
+  [%expect {| 58 |}]
+;;
+
+let%expect_test "Day 18.2" =
+  Format.printf "%i" @@ solve_part_2 @@ Utils.lines_of_input 18;
+  [%expect {| 2060 |}]
+;;

src/grid.ml

@@ -27,13 +27,15 @@ let at grid point =
 ;;
 
 let at_e (grid : 'a t) (point : Vec2.t) =
-  Option.get_exn_or "point out of bounds!" @@ at grid point
+  match at grid point with
+  | Some point -> point
+  | None -> failwith @@ Format.sprintf "point %a out of bounds!" Vec2.pp point
 ;;
 
 let set_e grid point item =
   if in_bounds grid point
   then Array.set grid.items (idx_of_vec2 grid.width point) item
-  else failwith "point out of bounds!"
+  else failwith (Format.sprintf "point %a out of bounds!" Vec2.pp point)
 ;;
 
 let ( .%() ) = at
@@ -82,12 +84,16 @@ let iter grid callback =
   iter_region grid a b callback
 ;;
 
-let draw grid printer =
-  let str = ref [] in
+let draw grid ?(rev_y = false) ?(rev_x = false) printer =
+  let line = ref [] in
+  let lines = ref [] in
   iter grid (fun point ->
     let item = grid.%(point) in
-    let char = printer @@ Option.get_exn_or "iter is broken" item in
-    str := !str @ [ char ];
-    if point.x = grid.width - 1 then str := !str @ [ '\n' ]);
-  String.of_list !str
+    let char = printer point (Option.get_exn_or "iter is broken" item) in
+    line := if rev_x then char :: !line else !line @ [ char ];
+    if List.length !line = grid.width
+    then (
+      lines := !lines @ [ String.of_list !line ];
+      line := []));
+  String.concat "\n" (if rev_y then List.rev !lines else !lines)
 ;;

src/grid.mli

@@ -11,4 +11,4 @@ val find : 'a t -> ('a -> bool) -> (Vec2.t * 'a) option
 val count : 'a t -> ('a -> bool) -> int
 val iter_region : 'a t -> Vec2.t -> Vec2.t -> (Vec2.t -> unit) -> unit
 val iter : 'a t -> (Vec2.t -> unit) -> unit
-val draw : 'a t -> ('a -> char) -> string
+val draw : 'a t -> ?rev_y:bool -> ?rev_x:bool -> (Vec2.t -> 'a -> char) -> string

src/utils.ml

@@ -10,6 +10,106 @@ let lines_of_input day =
   IO.(with_in path read_lines_l)
 ;;
 
+(** [f] in [memo f] should be a function that makes recursive calls
+    via the memoized function passed as its first argument. ie:
+    {[
+      let fib_m =
+        memo (fun self x ->
+          match x with
+          | 0 | 1 -> 1
+          | x -> self (x - 1) + self (x - 2))
+      ;;
+    ]} *)
+let memo f =
+  let open Hashtbl in
+  let cache = create 100000 in
+  let rec f_mem k =
+    try find cache k with
+    | Not_found ->
+      let v = f f_mem k in
+      add cache k v;
+      v
+  in
+  f_mem
+;;
+
+let%expect_test "fib memoized" =
+  let fib_m =
+    memo (fun fib_m x ->
+      match x with
+      | 0 | 1 -> 1
+      | x -> fib_m (x - 1) + fib_m (x - 2))
+  in
+  Printf.printf "%i\n" @@ fib_m 100;
+  [%expect {| 1298777728820984005 |}]
+;;
+
+let djikstra ~eq ~get_info ~set_info ~get_weight ~get_neighbors ~goal ~start_nodes =
+  let seen = ref [] in
+  let rec djikstra' c_node =
+    let c_dist, _ = get_info c_node in
+    set_info c_node (c_dist, true);
+    get_neighbors c_node
+    |> Iter.iter (fun neighbor ->
+      let n_dist, n_visited = get_info neighbor in
+      if not n_visited
+      then (
+        let new_dist = c_dist + get_weight c_node neighbor in
+        if new_dist < n_dist then set_info neighbor (new_dist, n_visited);
+        seen := List.add_nodup ~eq neighbor !seen));
+    seen
+    := List.fast_sort
+         (fun a b ->
+           let a_dist, _ = get_info a in
+           let b_dist, _ = get_info b in
+           Int.compare a_dist b_dist)
+         !seen;
+    match goal, !seen with
+    | Some goal_node, next :: _ when eq goal_node next ->
+      let dist, _ = get_info next in
+      Some dist
+    | None, [] -> Some 0
+    | _, next :: rest ->
+      seen := rest;
+      djikstra' next
+    | Some _, [] -> None
+  in
+  List.iter (fun node -> set_info node (0, false)) start_nodes;
+  match start_nodes with
+  | first :: rest ->
+    seen := rest;
+    djikstra' first
+  | _ -> failwith "start_nodes cannot be empty"
+;;
+
+let djikstra_hash
+  (type k)
+  ?(hash = Hashtbl.hash)
+  ?(eq = Stdlib.( = ))
+  ?(slots = 100)
+  ~get_weight
+  ~get_neighbors
+  ~start_nodes
+  ()
+  =
+  let module Tbl =
+    CCHashtbl.Make (struct
+      type t = k
+
+      let equal = eq
+      let hash = hash
+    end)
+  in
+  let table = Tbl.create slots in
+  let get_info node = Tbl.get_or ~default:(Int.max_int, false) table node in
+  let set_info node info = Tbl.replace table node info in
+  let dist_of node = Option.(Tbl.get table node >|= fun (dist, _) -> dist) in
+  let _ =
+    djikstra ~eq ~get_info ~set_info ~get_weight ~get_neighbors ~goal:None ~start_nodes
+  in
+  dist_of
+;;
+
 module Parse = struct
   include Angstrom
 

src/vec2.ml

@@ -35,10 +35,10 @@ let fold_region a b callback init =
   !acc
 ;;
 
-let bounds padding points =
+let find_bounds padding points =
   let lx, hx, ly, hy =
     points
-    |> List.fold_left
+    |> Iter.fold
          (fun (lx, hx, ly, hy) { x; y } ->
            let lx = min lx x in
            let hx = max hx x in

src/vec2.mli

@@ -20,5 +20,5 @@ val ( = ) : t -> t -> bool
 val abs : t -> t
 val iter_region : t -> t -> (t -> unit) -> unit
 val fold_region : t -> t -> ('a -> t -> 'a) -> 'a -> 'a
-val bounds : int -> t list -> t * t
+val find_bounds : int -> t Iter.t -> t * t
 val in_bounds : t -> t -> t -> bool