From d1188699e5c26918c398a11cc51d1bf8821dbb09 Mon Sep 17 00:00:00 2001
From: Jordan Doyle <jordan@doyle.la>
Date: Fri, 13 Dec 2024 02:43:10 +0000
Subject: [PATCH] Add 2024 day 11

---
 README     |  4 ++--
 2024/11.ml | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/README b/README
index 5e855a0..0a04c45 100644
--- a/README
+++ a/README
@@ -24,8 +24,8 @@
 |        8 | Rust     | |        8 | Haskell  |
 |        9 | OCaml    | |        9 | Haskell  |
 |       10 | OCaml    | |       10 | Haskell  |
-+---------------------+ |       11 | Haskell  |
-                        |       12 | Rust     |
+|       11 | OCaml    | |       11 | Haskell  |
++---------------------+ |       12 | Rust     |
                         |       13 | Haskell  |
                         |       14 | Haskell  |
                         |       15 | Haskell  |
diff --git a/2024/11.ml b/2024/11.ml
new file mode 100755
index 0000000..b3779ef 100755
--- /dev/null
+++ a/2024/11.ml
@@ -1,0 +1,49 @@
+#!/usr/bin/env nix-shell
+
+(*
+#!nix-shell --pure -i ocaml -p ocaml
+*)
+
+let input = read_line () |> String.split_on_char ' ' |> List.map int_of_string
+
+let rec pow a = function
+  | 0 ->
+      1
+  | 1 ->
+      a
+  | n ->
+      let b = pow a (n / 2) in
+      b * b * if n mod 2 = 0 then 1 else a
+
+let transform = function
+  | 0 ->
+      [1]
+  | n ->
+      let log10 = Float.(to_int (log10 (of_int n))) + 1 in
+      let exp = pow 10 (log10 / 2) in
+      let lhs = n / exp in
+      let rhs = n - (lhs * exp) in
+      if log10 mod 2 = 0 then [lhs; rhs] else [n * 2024]
+
+let count n x =
+  let memo = Hashtbl.create 100 in
+  let rec aux n x =
+    match (n, Hashtbl.find_opt memo (n, x)) with
+    | _, Some v ->
+        v
+    | 0, _ ->
+        1
+    | n, _ ->
+        let res =
+          transform x |> List.map (aux (n - 1)) |> List.fold_left ( + ) 0
+        in
+        Hashtbl.add memo (n, x) res ;
+        res
+  in
+  aux n x
+
+let iter n = input |> List.map (count n) |> List.fold_left ( + ) 0
+
+let _ = iter 25 |> print_int |> print_newline
+
+let _ = iter 75 |> print_int |> print_newline
--
rgit 0.1.5