faster 15.2 solution with line intersections :/
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ryan
parent
8d97e7601c
commit
705c9e9a7c
138
src/day15.ml
138
src/day15.ml
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@ -1,5 +1,4 @@
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open Containers
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module VecTbl = Hashtbl.Make (Vec2)
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type sensor =
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{ pos : Vec2.t
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@ -53,8 +52,9 @@ let bounds sensors =
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;;
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let could_be_beacon sensors ignore_known pos =
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sensors
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|> List.fold_while
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let open Iter in
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of_list sensors
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|> fold_while
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(fun _ s ->
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let d = taxicab_dist pos s.pos in
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if d <= s.dist && (ignore_known || not Vec2.(pos = s.beacon))
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@ -63,61 +63,103 @@ let could_be_beacon sensors ignore_known pos =
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true
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;;
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let%expect_test "Day 15.1" =
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let sensors = Utils.lines_of_input 15 |> List.map parse_sensor in
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let scan_row = 2000000 in
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let Vec2.{ x = lx; _ }, Vec2.{ x = hx; _ } = bounds sensors in
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Vec2.fold_region
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Vec2.{ x = lx; y = scan_row }
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Vec2.{ x = hx; y = scan_row }
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(fun acc pos -> if could_be_beacon sensors false pos then acc else acc + 1)
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0
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|> Printf.printf "%i\n";
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[%expect {| 5525990 |}]
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;;
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(* let%expect_test "Day 15.1" = *)
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(* let sensors = Utils.lines_of_input 15 |> List.map parse_sensor in *)
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(* let scan_row = 2000000 in *)
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(* let Vec2.{ x = lx; _ }, Vec2.{ x = hx; _ } = bounds sensors in *)
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(* Vec2.fold_region *)
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(* Vec2.{ x = lx; y = scan_row } *)
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(* Vec2.{ x = hx; y = scan_row } *)
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(* (fun acc pos -> if could_be_beacon sensors false pos then acc else acc + 1) *)
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(* 0 *)
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(* |> Printf.printf "%i\n"; *)
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(* [%expect {| 5525990 |}] *)
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(* ;; *)
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let points_on_border tbl sensor =
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let points = ref [] in
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let dist = sensor.dist + 1 in
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for d1 = 0 to dist do
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let d2 = dist - d1 in
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let open Vec2 in
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let p1 = of_tuple (d1, d2) in
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let p2 = of_tuple (d1, Int.(-d2)) in
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let new_points =
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[ sensor.pos + p1; sensor.pos - p1; sensor.pos + p2; sensor.pos - p2 ]
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|> List.fold_left
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(fun acc point ->
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match VecTbl.mem tbl point with
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| true -> point :: acc
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| false ->
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VecTbl.add tbl point ();
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acc)
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[]
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in
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points := !points @ new_points
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done;
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!points
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;;
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(* module VecTbl = Hashtbl.Make (Vec2) *)
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(* let points_on_border tbl sensor = *)
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(* let points = ref [] in *)
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(* let dist = sensor.dist + 1 in *)
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(* for d1 = 0 to dist do *)
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(* let d2 = dist - d1 in *)
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(* let open Vec2 in *)
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(* let p1 = of_tuple (d1, d2) in *)
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(* let p2 = of_tuple (d1, Int.(-d2)) in *)
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(* let new_points = *)
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(* [ sensor.pos + p1; sensor.pos - p1; sensor.pos + p2; sensor.pos - p2 ] *)
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(* |> List.fold_left *)
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(* (fun acc point -> *)
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(* match VecTbl.find_opt tbl point with *)
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(* | Some false -> acc *)
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(* | Some true -> *)
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(* VecTbl.replace tbl point false; *)
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(* point :: acc *)
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(* | None -> *)
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(* VecTbl.add tbl point true; *)
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(* acc) *)
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(* [] *)
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(* in *)
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(* points := !points @ new_points *)
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(* done; *)
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(* !points *)
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(* ;; *)
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(* let%expect_test "Day 15.2 brute force" = *)
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(* let sensors = Utils.lines_of_input 15 |> List.map parse_sensor in *)
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(* let mult = 4000000 in *)
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(* let range = mult in *)
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(* let in_bounds = Vec2.(in_bounds origin @@ of_tuple (range, range)) in *)
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(* let tbl = VecTbl.create (range * 10) in *)
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(* let point = *)
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(* sensors *)
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(* |> Iter.of_list *)
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(* |> Iter.flat_map_l @@ points_on_border tbl *)
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(* |> Iter.fold_while *)
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(* (fun _ v -> *)
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(* if in_bounds v && could_be_beacon sensors true v *)
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(* then Some v, `Stop *)
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(* else None, `Continue) *)
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(* None *)
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(* |> Option.get_exn_or "fucc :(" *)
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(* in *)
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(* Printf.printf "%i\n" ((mult * point.x) + point.y); *)
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(* [%expect {| 11756174628223 |}] *)
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(* ;; *)
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module IntSet = Set.Make (Int)
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let%expect_test "Day 15.2" =
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let sensors = Utils.lines_of_input 15 |> List.map parse_sensor in
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let mult = 4000000 in
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let range = mult in
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let in_bounds = Vec2.(in_bounds origin @@ of_tuple (range, range)) in
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let tbl = VecTbl.create (range * 10) in
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let point =
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let pos_coeffs, neg_coeffs =
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sensors
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|> Iter.of_list
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|> Iter.flat_map_l @@ points_on_border tbl
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|> Iter.fold_while
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(fun _ v ->
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if in_bounds v && could_be_beacon sensors true v
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then Some v, `Stop
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|> Iter.fold
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(fun (pos_coeffs, neg_coeffs) { pos; beacon = _; dist } ->
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let p1 = pos.y - pos.x + dist + 1 in
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let p2 = pos.y - pos.x - dist - 1 in
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let n1 = pos.y + pos.x + dist + 1 in
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let n2 = pos.y + pos.x - dist - 1 in
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Iter.(
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( append pos_coeffs (of_list [ p1; p2 ])
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, append neg_coeffs (of_list [ n1; n2 ]) )))
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(Iter.empty, Iter.empty)
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in
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let point =
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let open Iter in
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product pos_coeffs neg_coeffs
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|> fold_while
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(fun _ (p, n) ->
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let i = Vec2.of_tuple ((n - p) / 2, (n + p) / 2) in
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if in_bounds i && could_be_beacon sensors true i
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then Some i, `Stop
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else None, `Continue)
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None
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|> Option.get_exn_or "fucc :("
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|> Option.get_exn_or "no distress beacon found :("
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in
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Printf.printf "%i" ((mult * point.x) + point.y);
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[%expect {| 11756174628223|}]
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Printf.printf "%i\n" ((mult * point.x) + point.y);
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[%expect {| 11756174628223 |}]
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;;
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