2024 day 3 part 1 looks reasonable now.

bin/day2423.ml

@@ -20,25 +20,24 @@ let load_file fname =
   |> List.map make_pairs
   |> List.fold_left add_connection StringMap.empty
 
-let rec find_second_member acc connections visited a =
-  let rec impl acc a b = function
+let rec find_second_member acc connections visited a candidates =
+  let rec impl acc set = function
     | [] -> acc
-    | c :: t -> impl (StringSet.of_list [ a; b; c ] :: acc) a b t
+    | c :: t -> impl (StringSet.add c set :: acc) set t
   in
-  function
-  | [] -> acc
-  | h :: t ->
+  match StringSet.choose_opt candidates with
+  | None -> acc
+  | Some h ->
+      let candidates = StringSet.remove h candidates in
       if StringSet.mem h visited then
-        find_second_member acc connections visited a t
+        find_second_member acc connections visited a candidates
       else
         let visited = StringSet.add h visited in
-        let anh =
-          StringSet.inter
-            (StringMap.find a connections)
-            (StringMap.find h connections)
+        let anh = StringSet.inter (StringMap.find h connections) candidates in
+        let acc =
+          impl acc (StringSet.of_list [ a; h ]) (StringSet.to_list anh)
         in
-        let acc = impl acc a h (StringSet.to_list anh) in
-        find_second_member acc connections visited a t
+        find_second_member acc connections visited a candidates
 
 let rec find_rings acc visited connections = function
   | [] -> acc
@@ -48,7 +47,7 @@ let rec find_rings acc visited connections = function
         let visited = StringSet.add h visited in
         let acc =
           find_second_member acc connections visited h
-            (StringSet.to_list (StringMap.find h connections))
+            (StringMap.find h connections)
         in
         find_rings acc visited connections t
 
@@ -56,14 +55,11 @@ let rec find_rings acc visited connections = function
     letter ['t']. *)
 let starts_with_t set = StringSet.exists (fun x -> x.[0] = 't') set
 
-let set_compare a b = compare (StringSet.elements a) (StringSet.elements b)
-
 let part1 connections =
   StringMap.to_list connections
   |> List.map fst
   |> find_rings [] StringSet.empty connections
-  |> List.filter starts_with_t |> List.sort_uniq set_compare |> List.length
-  |> string_of_int
+  |> List.filter starts_with_t |> List.length |> string_of_int
 
 (** [search_candidate max_lst connections current candidates] searches for the
     longest star network that contains all the computers in [current] and maybe