Day 7

1 files changed, 38 insertions, 0 deletions

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+(*
+ * 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