Day 7

3 files changed, 40 insertions, 0 deletions

diff --git a/bin/main.ml b/bin/main.ml
index ebde0e3..fb1c28e 100644
--- a/bin/main.ml
+++ b/bin/main.ml
@@ -38,6 +38,8 @@ let day_part_fn day part =
   | 5, 2 -> Day05.part2
   | 6, 1 -> Day06.part1
   | 6, 2 -> Day06.part2
+  | 7, 1 -> Day07.part1
+  | 7, 2 -> Day07.part2
   | _ ->
       failwith
         (Format.sprintf "Day %d, part %d, has not yet been implemented\n" day
diff --git a/data b/data
-Subproject fade3292f33ea16f360782f0c55d3ce2b72ea5a
+Subproject 472b90e921b561b5e58effab41ea99690b5e5b9
diff --git a/lib/day07.ml b/lib/day07.ml
new file mode 100644
index 0000000..56de649
--- /dev/null
+++ b/lib/day07.ml
@@ -0,0 +1,38 @@
+(*
+ * SPDX-FileCopyrightText: Copyright 2025 Alexandre Jesus <https://adbjesus.com>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *)
+
+let solve transition_fn answer_fn ch =
+  (* the following assumes tachyon splitters are not adjacent *)
+  (* it also assume that the input is a perfect grid *)
+  let lines = In_channel.input_lines ch in
+  let start = String.index (List.hd lines) 'S' in
+  let m = String.length (List.hd lines) in
+  let cur = Array.make m 0 in
+  cur.(start) <- 1;
+  List.iter (String.iteri (transition_fn cur)) (List.tl lines);
+  Printf.printf "%d\n" (answer_fn cur)
+
+let part1 ch =
+  let ans = ref 0 in
+  let transition_fn cur j c =
+    if c = '^' then (
+      cur.(j - 1) <- Int.logor cur.(j - 1) cur.(j);
+      cur.(j + 1) <- Int.logor cur.(j + 1) cur.(j);
+      ans := !ans + cur.(j);
+      cur.(j) <- 0)
+  in
+  let answer_fn _cur = !ans in
+  solve transition_fn answer_fn ch
+
+let part2 ch =
+  let transition_fn cur j c =
+    if c = '^' then (
+      cur.(j - 1) <- cur.(j - 1) + cur.(j);
+      cur.(j + 1) <- cur.(j + 1) + cur.(j);
+      cur.(j) <- 0)
+  in
+  let answer_fn cur = Array.fold_left ( + ) 0 cur in
+  solve transition_fn answer_fn ch