From 33d7b340028d8ef813623e23d082083288d0c793 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Thu, 19 Dec 2024 11:06:02 +0000
Subject: [PATCH] 2024 day 19 part 1

---
 bin/day2419.ml | 44 ++++++++++++++++++++++++++++++++++++++++++++
 bin/dune       |  6 ++++--
 2 files changed, 48 insertions(+), 2 deletions(-)
 create mode 100644 bin/day2419.ml

diff --git a/bin/day2419.ml b/bin/day2419.ml
new file mode 100644
index 0000000..c0ec9ab
--- /dev/null
+++ b/bin/day2419.ml
@@ -0,0 +1,44 @@
+(** [towels_of_strings lst] returns a pair containing a list of available towels
+    and a list of patterns wanted. *)
+let towels_of_strings = function
+  | h :: "" :: t ->
+      let re = Str.regexp "[, ]+" in
+      let h = Str.split re h in
+      (h, t)
+  | _ -> failwith "towels_of_strings"
+
+let towels_of_file fname = Aoc.strings_of_file fname |> towels_of_strings
+let memo = Hashtbl.create 1000
+
+let rec memoize_has_pattern pattern towels =
+  let pattern_len = String.length pattern in
+  let rec has_pattern = function
+    | [] -> false
+    | h :: t ->
+        let towel_len = String.length h in
+        if String.starts_with ~prefix:h pattern then
+          memoize_has_pattern
+            (String.sub pattern towel_len (pattern_len - towel_len))
+            towels
+          || has_pattern t
+        else has_pattern t
+  in
+  match Hashtbl.find_opt memo pattern with
+  | Some x -> x
+  | None ->
+      let x = if pattern_len = 0 then true else has_pattern towels in
+      Hashtbl.add memo pattern x;
+      x
+
+let has_match towels pattern = memoize_has_pattern pattern towels
+
+let part1 (towels, patterns) =
+  List.filter
+    (fun p ->
+      let x = has_match towels p in
+      flush stdout;
+      x)
+    patterns
+  |> List.length
+
+let _ = Aoc.main towels_of_file [ (string_of_int, part1) ]
diff --git a/bin/dune b/bin/dune
index 625b669..c24ba0f 100644
--- a/bin/dune
+++ b/bin/dune
@@ -17,7 +17,8 @@
   day2415
   day2416
   day2417
-  day2418)
+  day2418
+  day2419)
  (names
   day2401
   day2402
@@ -36,5 +37,6 @@
   day2415
   day2416
   day2417
-  day2418)
+  day2418
+  day2419)
  (libraries str aoc))