Add 2024 day 24 part 2

For part 2 we only use helper functions most of the calculations are
done manually.

bin/day2424.ml

@@ -0,0 +1,134 @@
+type op = And | Or | Xor
+type gate = { in1 : string; in2 : string; op : op; out : string }
+
+module StringMap = Map.Make (String)
+
+let get_wire_value str =
+  let re = Str.regexp {|\(.+\): \([01]\)|} in
+  let _ = Str.search_forward re str 0 in
+  let v = if Str.matched_group 2 str = "0" then 0 else 1 in
+  (Str.matched_group 1 str, v)
+
+let get_gate_op = function
+  | "AND" -> And
+  | "OR" -> Or
+  | "XOR" -> Xor
+  | _ -> failwith "get_gate_op"
+
+let[@warning "-32"] string_of_op = function
+  | And -> "AND"
+  | Or -> "OR"
+  | Xor -> "XOR"
+
+let get_gate_config str =
+  let re = Str.regexp {|\(.+\) \(AND\|OR\|XOR\) \(.+\) -> \(.+\)|} in
+  let _ = Str.search_forward re str 0 in
+  let in1 = Str.matched_group 1 str in
+  let op = get_gate_op (Str.matched_group 2 str) in
+  let in2 = Str.matched_group 3 str in
+  let out = Str.matched_group 4 str in
+  { in1; in2; op; out }
+
+let initial_wires_of_strings =
+  let rec impl acc = function
+    | "" :: t -> (acc, t)
+    | h :: t ->
+        let wire, v = get_wire_value h in
+        impl (StringMap.add wire v acc) t
+    | _ -> failwith "initial_wires_of_strings"
+  in
+  impl StringMap.empty
+
+let gates_from_strings =
+  let rec impl acc = function
+    | [] -> acc
+    | h :: t -> impl (get_gate_config h :: acc) t
+  in
+  impl []
+
+let config_of_file fname =
+  let lst = Aoc.strings_of_file fname in
+  let wires, lst = initial_wires_of_strings lst in
+  let gates = gates_from_strings lst in
+  (wires, gates)
+
+let process_gate wires gate =
+  match
+    ( gate.op,
+      StringMap.find_opt gate.in1 wires,
+      StringMap.find_opt gate.in2 wires )
+  with
+  | And, Some a, Some b -> if a = 1 && b = 1 then Some 1 else Some 0
+  | Or, Some a, Some b -> if a = 1 || b = 1 then Some 1 else Some 0
+  | Xor, Some a, Some b -> if a <> b then Some 1 else Some 0
+  | _, _, _ -> None
+
+let process_gates wires =
+  let rec impl wires acc = function
+    | [] -> (wires, acc)
+    | h :: t -> begin
+        match process_gate wires h with
+        | None -> impl wires (h :: acc) t
+        | Some x ->
+            let wires = StringMap.add h.out x wires in
+            impl wires acc t
+      end
+  in
+  impl wires []
+
+let rec repeat_to_end wires gates =
+  let old_len = List.length gates in
+  let wires, gates = process_gates wires gates in
+  if gates = [] then Some wires
+  else if old_len = List.length gates then begin
+    Printf.printf "Loop detected: %d\n" (List.length gates);
+    None
+  end
+  else begin
+    repeat_to_end wires gates
+  end
+
+let calc_value = Fun.flip (List.fold_right (fun x acc -> x + (2 * acc))) 0
+
+let k_wires wires x =
+  StringMap.filter (fun k _ -> k.[0] = x) wires
+  |> StringMap.bindings |> List.map snd |> calc_value
+
+let wires_set wires x v' =
+  let set_v k v =
+    if k.[0] = x then
+      let idx = int_of_string (String.sub k 1 (String.length k - 1)) in
+      (v' lsr idx) land 1
+    else v
+  in
+  StringMap.mapi set_v wires
+
+let part1 (wires, gates) =
+  match repeat_to_end wires gates with
+  | None -> failwith "part1"
+  | Some wires -> k_wires wires 'z'
+
+let part2 (wires, gates) =
+  let run_test x y =
+    let wires = wires_set wires 'x' x in
+    let wires = wires_set wires 'y' y in
+    Printf.printf "%d + %d = " (k_wires wires 'x') (k_wires wires 'y');
+    match repeat_to_end wires gates with
+    | None -> print_endline "(infinite loop)"
+    | Some wires ->
+        let z = k_wires wires 'z' in
+        print_int z;
+        if z <> x + y then print_string " (wrong answer)";
+        print_newline ()
+  in
+  let tst n =
+    Printf.printf "Test for n = %d\n" n;
+    run_test (1 lsl n) 0;
+    run_test 0 (1 lsl n);
+    run_test (1 lsl n) (1 lsl n)
+  in
+  Seq.ints 0 |> Seq.take 45 |> Seq.iter tst;
+  0
+
+let _ =
+  Aoc.main config_of_file [ (string_of_int, part1); (string_of_int, part2) ]

bin/dune

@@ -22,7 +22,8 @@
   day2420
   day2421
   day2422
-  day2423)
+  day2423
+  day2424)
  (names
   day2401
   day2402
@@ -46,5 +47,6 @@
   day2420
   day2421
   day2422
-  day2423)
+  day2423
+  day2424)
  (libraries str aoc))