From 71c5b5e5a2684edefa2e7b516143aadc197c6926 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Sun, 8 Dec 2024 08:09:20 +0000
Subject: [PATCH] 2024 day 8 part 1

---
 bin/day2408.ml | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++
 bin/dune       | 12 ++++++--
 2 files changed, 85 insertions(+), 2 deletions(-)
 create mode 100644 bin/day2408.ml

diff --git a/bin/day2408.ml b/bin/day2408.ml
new file mode 100644
index 0000000..d378503
--- /dev/null
+++ b/bin/day2408.ml
@@ -0,0 +1,75 @@
+type map = { map : string; width : int; height : int }
+
+let map_of_file fname =
+  let strs = Aoc.strings_of_file fname in
+  let width = String.length (List.hd strs) in
+  let map = List.fold_left ( ^ ) "" strs in
+  let height = String.length map / width in
+  { map; width; height }
+
+let map_length map = String.length map.map
+let map_get_by_idx map idx = map.map.[idx]
+let map_pos_of_idx map idx = (idx mod map.width, idx / map.width)
+let map_idx_of_pos map (x, y) = x + (y * map.width)
+(*let map_get_pos map pos = map_get_by_idx map (map_idx_of_pos map pos)*)
+
+let map_is_valid_pos map (x, y) =
+  x >= 0 && x < map.width && y >= 0 && y < map.height
+
+(*let map_is_valid_idx map idx = idx >= 0 && idx < map_length map*)
+
+let get_station_indices map =
+  let arr = Array.make 256 [] in
+  let rec impl idx =
+    if idx >= map_length map then arr
+    else if map_get_by_idx map idx = '.' then impl (idx + 1)
+    else
+      let station = int_of_char (map_get_by_idx map idx) in
+      arr.(station) <- idx :: arr.(station);
+      impl (idx + 1)
+  in
+  impl 0
+
+let get_antinodes map station_idxs =
+  let rec impl2 acc (px, py) = function
+    | [] -> acc
+    | h :: t ->
+        let hx, hy = map_pos_of_idx map h in
+        let dx = hx - px in
+        let dy = hy - py in
+        impl2 ((px - dx, py - dy) :: (hx + dx, hy + dy) :: acc) (px, py) t
+  in
+  let rec impl acc = function
+    | [] -> acc
+    | h :: t -> impl (impl2 acc (map_pos_of_idx map h) t) t
+  in
+  let lst = impl [] station_idxs |> List.filter (map_is_valid_pos map) in
+  let lst2 = lst |> List.map (map_idx_of_pos map) in
+  lst2
+
+let process_stations map stations = Array.map (get_antinodes map) stations
+
+let string_replace str pos c =
+  assert (pos < String.length str);
+  String.sub str 0 pos ^ String.make 1 c
+  ^ String.sub str (pos + 1) (String.length str - pos - 1)
+
+let map_print map =
+  let rec impl off = if off < map_length map then impl (off + map.width) in
+  impl 0
+
+let rec add_stations map = function
+  | [] -> map
+  | h :: t -> add_stations { map with map = string_replace map.map h '#' } t
+
+let part1 map =
+  let lst =
+    get_station_indices map |> process_stations map
+    |> Array.fold_left List.append []
+    |> List.sort_uniq Stdlib.compare
+  in
+  let map' = add_stations map lst in
+  map_print map';
+  List.length lst
+
+let _ = Aoc.main map_of_file [ (string_of_int, part1) ]
diff --git a/bin/dune b/bin/dune
index b674f78..8536833 100644
--- a/bin/dune
+++ b/bin/dune
@@ -1,4 +1,12 @@
 (executables
- (public_names day2401 day2402 day2403 day2404 day2405 day2406 day2407)
- (names day2401 day2402 day2403 day2404 day2405 day2406 day2407)
+ (public_names
+  day2401
+  day2402
+  day2403
+  day2404
+  day2405
+  day2406
+  day2407
+  day2408)
+ (names day2401 day2402 day2403 day2404 day2405 day2406 day2407 day2408)
  (libraries str aoc))