From 030fd73babc9eb401a5b444748042ffcff307616 Mon Sep 17 00:00:00 2001
From: Matthew Gretton-Dann <matt@gretton-dann.org.uk>
Date: Tue, 24 Dec 2024 20:23:23 +0000
Subject: [PATCH] Add 2024 day 24 part 2

For part 2 we only use helper functions most of the calculations are
done manually.
---
 bin/day2424.ml | 55 ++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 47 insertions(+), 8 deletions(-)

diff --git a/bin/day2424.ml b/bin/day2424.ml
index 064d190..136cd8b 100644
--- a/bin/day2424.ml
+++ b/bin/day2424.ml
@@ -77,19 +77,58 @@ let process_gates wires =
   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 wires
+  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
-    Printf.printf "Gate size: %d\n" (List.length gates);
     repeat_to_end wires gates
   end
 
 let calc_value = Fun.flip (List.fold_right (fun x acc -> x + (2 * acc))) 0
 
-let part1 (wires, gates) =
-  let wires = repeat_to_end wires gates in
-  let zmap = StringMap.filter (fun k _ -> k.[0] = 'z') wires in
-  let zlst = StringMap.bindings zmap |> List.map snd in
-  calc_value zlst
+let k_wires wires x =
+  StringMap.filter (fun k _ -> k.[0] = x) wires
+  |> StringMap.bindings |> List.map snd |> calc_value
 
-let _ = Aoc.main config_of_file [ (string_of_int, part1) ]
+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) ]