Added solution for "Day 20: Pulse Propagation", part 2

solvers/UPulsePropagation.pas

@@ -1,6 +1,6 @@
 {
   Solutions to the Advent Of Code.
-  Copyright (C) 2023  Stefan Müller
+  Copyright (C) 2023-2024  Stefan Müller
 
   This program is free software: you can redistribute it and/or modify it under
   the terms of the GNU General Public License as published by the Free Software
@@ -22,7 +22,7 @@ unit UPulsePropagation;
 interface
 
 uses
-  Classes, SysUtils, Generics.Collections, Math, USolver;
+  Classes, SysUtils, Generics.Collections, USolver;
 
 type
   TModule = class;
@@ -49,12 +49,12 @@ type
   public
     property Name: string read FName;
     property OutputNames: TStringList read FOutputNames;
+    property Outputs: TModules read FOutputs;
     constructor Create(const AName: string);
     destructor Destroy; override;
     procedure AddInput(const AInput: TModule); virtual;
     procedure AddOutput(const AOutput: TModule); virtual;
     function ReceivePulse(const ASender: TModule; const AIsHigh: Boolean): TPulses; virtual; abstract;
-    function IsOff: Boolean; virtual;
   end;
 
   { TBroadcasterModule }
@@ -71,31 +71,29 @@ type
     FState: Boolean;
   public
     function ReceivePulse(const ASender: TModule; const AIsHigh: Boolean): TPulses; override;
-    function IsOff: Boolean; override;
   end;
 
-  { TConjectionBuffer }
+  { TConjunctionInputBuffer }
 
-  TConjectionBuffer = record
+  TConjunctionInputBuffer = record
     Input: TModule;
     LastState: Boolean;
   end;
 
-  TConjectionBuffers = specialize TList<TConjectionBuffer>;
+  TConjunctionInputBuffers = specialize TList<TConjunctionInputBuffer>;
 
   { TConjunctionModule }
 
   TConjunctionModule = class(TModule)
   private
-    FInputBuffers: TConjectionBuffers;
+    FInputBuffers: TConjunctionInputBuffers;
     procedure UpdateInputBuffer(constref AInput: TModule; const AState: Boolean);
-    function AreAllBuffersSame(const AIsHigh: Boolean): Boolean;
+    function AreAllBuffersHigh: Boolean;
   public
     constructor Create(const AName: string);
     destructor Destroy; override;
     procedure AddInput(const AInput: TModule); override;
     function ReceivePulse(const ASender: TModule; const AIsHigh: Boolean): TPulses; override;
-    function IsOff: Boolean; override;
   end;
 
   { TEndpointModule }
@@ -111,8 +109,6 @@ type
     LowCount, HighCount: Integer;
   end;
 
-  TButtonResults = specialize TList<TButtonResult>;
-
   { TPulsePropagation }
 
   TPulsePropagation = class(TSolver)
@@ -121,7 +117,7 @@ type
     FBroadcaster: TModule;
     procedure UpdateModuleConnections;
     function PushButton: TButtonResult;
-    function AreAllModulesOff: Boolean;
+    function CalcCounterTarget(const AFirstFlipFlop: TModule): Int64;
   public
     constructor Create;
     destructor Destroy; override;
@@ -180,11 +176,6 @@ begin
   FOutputs.Add(AOutput);
 end;
 
-function TModule.IsOff: Boolean;
-begin
-  Result := True;
-end;
-
 { TBroadcasterModule }
 
 function TBroadcasterModule.ReceivePulse(const ASender: TModule; const AIsHigh: Boolean): TPulses;
@@ -204,17 +195,12 @@ begin
   end;
 end;
 
-function TFlipFlopModule.IsOff: Boolean;
-begin
-  Result := not FState;
-end;
-
 { TConjunctionModule }
 
 procedure TConjunctionModule.UpdateInputBuffer(constref AInput: TModule; const AState: Boolean);
 var
   i: Integer;
-  buffer: TConjectionBuffer;
+  buffer: TConjunctionInputBuffer;
 begin
   for i := 0 to FInputBuffers.Count - 1 do
     if FInputBuffers[i].Input = AInput then
@@ -226,13 +212,13 @@ begin
     end;
 end;
 
-function TConjunctionModule.AreAllBuffersSame(const AIsHigh: Boolean): Boolean;
+function TConjunctionModule.AreAllBuffersHigh: Boolean;
 var
-  buffer: TConjectionBuffer;
+  buffer: TConjunctionInputBuffer;
 begin
   Result := True;
   for buffer in FInputBuffers do
-    if buffer.LastState <> AIsHigh then
+    if not buffer.LastState then
     begin
       Result := False;
       Exit;
@@ -242,7 +228,7 @@ end;
 constructor TConjunctionModule.Create(const AName: string);
 begin
   inherited Create(AName);
-  FInputBuffers := TConjectionBuffers.Create;
+  FInputBuffers := TConjunctionInputBuffers.Create;
 end;
 
 destructor TConjunctionModule.Destroy;
@@ -253,7 +239,7 @@ end;
 
 procedure TConjunctionModule.AddInput(const AInput: TModule);
 var
-  buffer: TConjectionBuffer;
+  buffer: TConjunctionInputBuffer;
 begin
   buffer.Input := AInput;
   buffer.LastState := False;
@@ -263,12 +249,7 @@ end;
 function TConjunctionModule.ReceivePulse(const ASender: TModule; const AIsHigh: Boolean): TPulses;
 begin
   UpdateInputBuffer(ASender, AIsHigh);
-  Result := CreatePulsesToOutputs(not AreAllBuffersSame(True));
-end;
-
-function TConjunctionModule.IsOff: Boolean;
-begin
-  Result := AreAllBuffersSame(False);
+  Result := CreatePulsesToOutputs(not AreAllBuffersHigh);
 end;
 
 { TEndpointModule }
@@ -342,17 +323,39 @@ begin
   queue.Free;
 end;
 
-function TPulsePropagation.AreAllModulesOff: Boolean;
+function TPulsePropagation.CalcCounterTarget(const AFirstFlipFlop: TModule): Int64;
 var
-  module: TModule;
+  binDigit: Int64;
+  current, next: TModule;
+  i: Integer;
 begin
-  Result := True;
-  for module in FModules do
-    if not module.IsOff then
+  Result := 0;
+  binDigit := 1;
+  current := AFirstFlipFlop;
+  while True do
+  begin
+    if current.Outputs.Count = 1 then
     begin
-      Result := False;
-      Exit;
+      current := current.Outputs.First;
+      if current is TConjunctionModule then
+      begin
+        Result := Result + binDigit;
+        Break;
+      end;
+    end
+    else begin
+      Result := Result + binDigit;
+      i := 0;
+      repeat
+        if i = current.Outputs.Count then
+          Exit;
+        next := current.Outputs[i];
+        Inc(i);
+      until next is TFlipFlopModule;
+      current := next;
     end;
+    binDigit := binDigit << 1;
+  end;
 end;
 
 constructor TPulsePropagation.Create;
@@ -392,42 +395,26 @@ end;
 
 procedure TPulsePropagation.Finish;
 var
-  results: TButtonResults;
-  finalResult: TButtonResult;
-  cycles, remainder, i, j, max: Integer;
+  result, accumulated: TButtonResult;
+  i: Integer;
+  module: TModule;
 begin
   UpdateModuleConnections;
 
-  // The pulse counts for the full puzzle input repeat themselves in a very specific way, but the system state does not.
-  // This indicates there is a better solution for this problem.
-  // TODO: See if there is a better solution based on the repeating patterns in the pulse counts.
-  results := TButtonResults.Create;
-  repeat
-    results.Add(PushButton);
-  until AreAllModulesOff or (results.Count >= CButtonPushes);
-
-  DivMod(CButtonPushes, results.Count, cycles, remainder);
-  finalResult.LowCount := 0;
-  finalResult.HighCount := 0;
-  max := results.Count - 1;
-  for j := 0 to 1 do
+  accumulated.LowCount := 0;
+  accumulated.HighCount := 0;
+  for i := 1 to CButtonPushes do
   begin
-    for i := 0 to max do
-    begin
-      Inc(finalResult.LowCount, results[i].LowCount);
-      Inc(finalResult.HighCount, results[i].HighCount);
-    end;
-    if j = 0 then
-    begin
-      finalResult.LowCount := finalResult.LowCount * cycles;
-      finalResult.HighCount := finalResult.HighCount * cycles;
-      max := remainder - 1;
-    end;
+    result := PushButton;
+    Inc(accumulated.LowCount, result.LowCount);
+    Inc(accumulated.HighCount, result.HighCount);
   end;
 
-  results.Free;
+  FPart1 := accumulated.LowCount * accumulated.HighCount;
 
-  FPart1 := finalResult.LowCount * finalResult.HighCount;
+  FPart2 := 1;
+  for module in FBroadcaster.Outputs do
+    FPart2 := FPart2 * CalcCounterTarget(module);
 end;
 
 function TPulsePropagation.GetDataFileName: string;