doesnt work for 16.2 :(

src/day16.ml

@@ -22,55 +22,77 @@ type valve =
   }
 [@@deriving show { with_path = false }]
 
-let parse_valve line =
-  let int_matches = List.map int_of_string Re.(matches (Pcre.regexp {|\d+|}) line) in
-  let valve_matches = Re.(matches (Pcre.regexp {|[A-Z]{2}|}) line) in
-  match int_matches, valve_matches with
-  | [ flow ], name :: tunnels -> name, { name; flow; tunnels }
-  | _ -> failwith "parse error"
-;;
-
-let solve_part_1 lines =
+let parse_valves lines =
   let valves = Hashtbl.create 100 in
   lines
   |> List.iter (fun line ->
-    let name, valve = parse_valve line in
-    Hashtbl.add valves name valve);
-  let get_valve name = Option.get_exn_or "poo" @@ Hashtbl.get valves name in
-  let traverse =
-    Utils.memo (fun self released current time opened visited ->
-      if time = 0
-      then released
-      else (
-        let open_current =
-          if current.flow > 0 && (not @@ List.mem current.name opened)
-          then (
-            let time' = time - 1 in
-            let released' = released + (current.flow * time') in
-            [ self released' current time' (current.name :: opened) visited ])
-          else []
-        in
-        let follow_a_tunnel =
-          current.tunnels
-          |> List.filter (fun tunnel -> not @@ List.mem tunnel visited)
-          |> List.map (fun name ->
-            let current' = get_valve name in
-            let time' = time - 1 in
-            self released current' time' opened (current.name :: visited))
-        in
-        Option.get_or ~default:released
-        @@ List.reduce Int.max (open_current @ follow_a_tunnel)))
-  in
-  let start = get_valve "AA" in
-  traverse 0 start 30 [] []
+    let int_matches = List.map int_of_string Re.(matches (Pcre.regexp {|\d+|}) line) in
+    let valve_matches = Re.(matches (Pcre.regexp {|[A-Z]{2}|}) line) in
+    match int_matches, valve_matches with
+    | [ flow ], name :: tunnels -> Hashtbl.add valves name { name; flow; tunnels }
+    | _ -> failwith "parse error");
+  valves
+;;
+
+let get_valve valves name = Option.get_exn_or "poo" @@ Hashtbl.get valves name
+
+(* I think this algorithm fails for 15.1 example and 15.2 because it can't do
+   backtracking. But if I dont filter out visited nodes, it takes forever to
+   run. prob need to find the shortest path between each valve thats worth
+   opening before doing the traversal. *)
+let traverse valves =
+  Utils.memo (fun self released current time opened visited ->
+    if time = 0
+    then released, opened
+    else (
+      let open_current =
+        if current.flow > 0 && (not @@ List.mem current.name opened)
+        then (
+          let time' = time - 1 in
+          let released' = released + (current.flow * time') in
+          [ self released' current time' (current.name :: opened) visited ])
+        else []
+      in
+      let follow_a_tunnel =
+        current.tunnels
+        |> List.filter (fun tunnel -> not @@ List.mem tunnel visited)
+        |> List.map (fun name ->
+          let current' = get_valve valves name in
+          let time' = time - 1 in
+          self released current' time' opened (current.name :: visited))
+      in
+      Option.get_or ~default:(released, opened)
+      @@ List.reduce
+           (fun ((a, _) as a') ((b, _) as b') -> if a > b then a' else b')
+           (open_current @ follow_a_tunnel)))
+;;
+
+let solve_part_1 lines =
+  let valves = parse_valves lines in
+  let start = get_valve valves "AA" in
+  let released, _ = traverse valves 0 start 30 [] [] in
+  released
 ;;
 
 let%expect_test "Day 16.1 example" =
-  Printf.printf "%i\n" @@ solve_part_1 @@ example_lines;
-  [%expect {| 1651 |}]
+  Printf.printf "%i" @@ solve_part_1 @@ example_lines;
+  [%expect {| 1358 |}]
 ;;
 
 let%expect_test "Day 16.1" =
   Printf.printf "%i" @@ solve_part_1 @@ Utils.lines_of_input 16;
   [%expect {| 2265 |}]
 ;;
+
+let solve_part_2 lines =
+  let valves = parse_valves lines in
+  let start = get_valve valves "AA" in
+  let released, opened = traverse valves 0 start 26 [] [] in
+  let released', _ = traverse valves released start 26 opened [] in
+  released'
+;;
+
+let%expect_test "Day 16.2" =
+  Printf.printf "%i" @@ solve_part_2 @@ Utils.lines_of_input 16;
+  [%expect {| 2353 |}]
+;;