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fix day 15 for example inputs

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part 1 didn't work for the example input :(
This commit is contained in:
ryan 2023-11-21 16:48:03 -08:00
parent 11546bff5f
commit 894e83fe12
1 changed files with 61 additions and 25 deletions
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86
src/day15.ml
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@ -1,5 +1,23 @@
open Containers
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"
; "Sensor at x=13, y=2: closest beacon is at x=15, y=3"
; "Sensor at x=12, y=14: closest beacon is at x=10, y=16"
; "Sensor at x=10, y=20: closest beacon is at x=10, y=16"
; "Sensor at x=14, y=17: closest beacon is at x=10, y=16"
; "Sensor at x=8, y=7: closest beacon is at x=2, y=10"
; "Sensor at x=2, y=0: closest beacon is at x=2, y=10"
; "Sensor at x=0, y=11: closest beacon is at x=2, y=10"
; "Sensor at x=20, y=14: closest beacon is at x=25, y=17"
; "Sensor at x=17, y=20: closest beacon is at x=21, y=22"
; "Sensor at x=16, y=7: closest beacon is at x=15, y=3"
; "Sensor at x=14, y=3: closest beacon is at x=15, y=3"
; "Sensor at x=20, y=1: closest beacon is at x=15, y=3"
]
;;
type sensor =
{ pos : Vec2.t
; beacon : Vec2.t
@ -51,24 +69,23 @@ let could_be_beacon sensors ignore_known pos =
n1 = y + bx + dist + 1
n2 = y + bx - dist - 1
]}*)
let get_consts sensors =
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 + 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
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)
;;
let%expect_test "Day 15.1" =
let sensors = Utils.lines_of_input 15 |> Iter.of_list |> Iter.map parse_sensor in
let scan_y = 2000000 in
let p_slope_consts, n_slope_consts = get_consts sensors in
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
@ -84,31 +101,41 @@ let%expect_test "Day 15.1" =
(Iter.map (fun n -> n - scan_y) n_slope_consts)
|> Iter.sort_uniq ~cmp:Int.compare
in
(* iterate thru the intersections by ascending x.
if a point in the region between two intersections can be a beacon,
then every point in the region can be. *)
let rec count_not_beacons count xs =
match xs with
| lx :: hx :: rest ->
let count =
if could_be_beacon sensors false @@ Vec2.of_tuple (lx + 1, scan_y)
then count
else count + hx - lx
| x :: next :: rest ->
let intersection =
if could_be_beacon sensors false @@ Vec2.of_tuple (x, scan_y) then 0 else 1
in
count_not_beacons count @@ (hx :: rest)
(* if there is a region between this intersection and the next, the value
of could_be_beacon is the same for each point within it. *)
let region =
if x + 1 < next && (could_be_beacon sensors false @@ Vec2.of_tuple (x + 1, scan_y))
then 0
else next - x - 1
in
count_not_beacons (count + intersection + region) (next :: rest)
| _ -> count
in
let possible_beacons = count_not_beacons 0 @@ Iter.to_list intersection_xs in
count_not_beacons 0 @@ Iter.to_list intersection_xs
;;
let%expect_test "Day 15.1 example" =
let possible_beacons = solve_part_1 example_lines 10 in
Printf.printf "%i\n" @@ possible_beacons;
[%expect {| 26 |}]
;;
let%expect_test "Day 15.1" =
let possible_beacons = solve_part_1 (Utils.lines_of_input 15) 2000000 in
Printf.printf "%i\n" @@ possible_beacons;
[%expect {| 5525990 |}]
;;
let%expect_test "Day 15.2" =
let sensors = Utils.lines_of_input 15 |> Iter.of_list |> Iter.map parse_sensor in
let mult = 4000000 in
let range = mult in
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 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.
@ -132,6 +159,15 @@ 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 |}]
;;