From 337f67717b231e0c550cfb74d79787f3d69ec53c Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Sun, 22 Dec 2024 09:44:28 +0000
Subject: [PATCH] 2024 day 22

---
 bin/day2422.ml | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++
 bin/dune       |  6 ++++--
 2 files changed, 62 insertions(+), 2 deletions(-)
 create mode 100644 bin/day2422.ml

diff --git a/bin/day2422.ml b/bin/day2422.ml
new file mode 100644
index 0000000..ca3c796
--- /dev/null
+++ b/bin/day2422.ml
@@ -0,0 +1,58 @@
+let next_secret secret =
+  let secret = secret * 64 lxor secret mod 16777216 in
+  let secret = secret / 32 lxor secret mod 16777216 in
+  let secret = secret * 2048 lxor secret mod 16777216 in
+  secret
+
+let nth_secret n secret =
+  let r = Aoc.apply_n n next_secret secret in
+  r
+
+let part1 n nums = List.map (nth_secret n) nums |> List.fold_left ( + ) 0
+
+module Int4Tuple = struct
+  type t = int * int * int * int
+
+  let compare = Stdlib.compare
+end
+
+module Int4Map = Map.Make (Int4Tuple)
+
+let secret_list n secret =
+  let rec impl s () = Seq.Cons (s, impl (next_secret s)) in
+  Seq.drop 1 (impl secret) |> Seq.take n |> List.of_seq
+
+let rec find_sequence_costs map =
+  let update_value amt = function None -> Some amt | x -> x in
+  function
+  | a :: b :: c :: d :: e :: t ->
+      find_sequence_costs
+        (Int4Map.update (b - a, c - b, d - c, e - d) (update_value e) map)
+        (b :: c :: d :: e :: t)
+  | _ -> map
+
+let part2 n secrets =
+  let merge_values _ x y =
+    match (x, y) with
+    | Some x, Some y -> Some (x + y)
+    | Some x, None -> Some x
+    | None, Some y -> Some y
+    | None, None -> None
+  in
+  let costs =
+    List.map (secret_list n) secrets
+    |> List.map (List.map (fun x -> x mod 10))
+    |> List.map (find_sequence_costs Int4Map.empty)
+    |> List.fold_left
+         (fun acc map -> Int4Map.merge merge_values acc map)
+         Int4Map.empty
+  in
+  Int4Map.fold (fun _ v acc -> max acc v) costs 0
+
+let read_file fname = Aoc.strings_of_file fname |> List.map int_of_string
+
+let _ =
+  Aoc.main read_file
+    [ (string_of_int, part1 2000); (string_of_int, part2 2000) ]
+
+(* 424 too low *)
diff --git a/bin/dune b/bin/dune
index ee1aa74..8f3149b 100644
--- a/bin/dune
+++ b/bin/dune
@@ -20,7 +20,8 @@
   day2418
   day2419
   day2420
-  day2421)
+  day2421
+  day2422)
  (names
   day2401
   day2402
@@ -42,5 +43,6 @@
   day2418
   day2419
   day2420
-  day2421)
+  day2421
+  day2422)
  (libraries str aoc))