From f1b143952426dd0e3efcecf541751ec7ffc04f6a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20M=C3=BCller?= <stefan.mueller@aksdb.de>
Date: Sat, 9 Dec 2023 14:46:35 +0100
Subject: [PATCH] Added solution for "Day 8: Haunted Wasteland", part 2

---
 solvers/UHauntedWasteland.pas        | 94 +++++++++++++++++-----------
 tests/UHauntedWastelandTestCases.pas | 41 ++++++++++++
 2 files changed, 97 insertions(+), 38 deletions(-)

diff --git a/solvers/UHauntedWasteland.pas b/solvers/UHauntedWasteland.pas
index 97d611c..fca5ab1 100644
--- a/solvers/UHauntedWasteland.pas
+++ b/solvers/UHauntedWasteland.pas
@@ -22,7 +22,7 @@ unit UHauntedWasteland;
 interface
 
 uses
-  Classes, SysUtils, Generics.Collections, USolver;
+  Classes, SysUtils, Generics.Collections, USolver, UNumberTheory;
 
 type
 
@@ -36,7 +36,7 @@ type
     constructor Create(const AName: string);
     property Name: string read FName;
     procedure AddNeighbors(constref ALeft, ARight: TNode);
-    function TryStep(const ADirection: Char; out ONewLocation: TNode): Boolean;
+    function Step(const ADirection: Char): TNode;
   end;
 
   TNodes = specialize TObjectList<TNode>;
@@ -47,10 +47,10 @@ type
   private
     FDirections: string;
     FNextDirectionIndex: Integer;
-    FNodes, FUnparsedNodes: TNodes;
-    FCurrentNode, FTargetNode: TNode;
+    FNodes, FUnparsedNodes, FGhostCurrentNodes: TNodes;
     procedure ProcessNode(const ALine: string);
     procedure DoSteps;
+    procedure IncDirectionIndex;
   public
     constructor Create;
     destructor Destroy; override;
@@ -77,23 +77,16 @@ begin
   FRight := ARight;
 end;
 
-function TNode.TryStep(const ADirection: Char; out ONewLocation: TNode): Boolean;
+function TNode.Step(const ADirection: Char): TNode;
 begin
-  ONewLocation := nil;
-  Result := False;
+  Result := nil;
   case ADirection of
     'L':
       if FLeft <> nil then
-      begin
-        ONewLocation := FLeft;
-        Result := True;
-      end;
+        Result := FLeft;
     'R':
       if FRight <> nil then
-      begin
-        ONewLocation := FRight;
-        Result := True;
-      end;
+        Result := FRight;
   end;
 end;
 
@@ -169,43 +162,71 @@ begin
 
   parsingNode.AddNeighbors(leftNode, rightNode);
 
-  // Checks for start and end nodes.
-  if name = 'ZZZ' then
-    FTargetNode := parsingNode
-  else if name = 'AAA' then
-    FCurrentNode := parsingNode;
+  // Checks for start nodes.
+  if name[3] = 'A' then
+    FGhostCurrentNodes.Add(parsingNode);
 end;
 
 procedure THauntedWasteland.DoSteps;
 var
-  new: TNode;
+  counts: specialize TList<Cardinal>;
+  gcd, count: Cardinal;
+  node, current: TNode;
 begin
-  if FCurrentNode <> nil then
+  gcd := 0;
+  counts := specialize TList<Cardinal>.Create;
+  counts.Capacity := FGhostCurrentNodes.Count;
+
+  for node in FGhostCurrentNodes do
   begin
-    while (FCurrentNode <> FTargetNode) and FCurrentNode.TryStep(FDirections[FNextDirectionIndex], new) do
-    begin
-      FCurrentNode := new;
-      Inc(FNextDirectionIndex);
-      if FNextDirectionIndex > Length(FDirections) then
-        FNextDirectionIndex := 1;
-      Inc(FPart1);
-    end;
+    current := node;
+    FNextDirectionIndex := 1;
+    count := 0;
+    repeat
+      current := current.Step(FDirections[FNextDirectionIndex]);
+      IncDirectionIndex;
+      Inc(count);
+    until current.Name[3] = 'Z';
+
+    if node.Name = 'AAA' then
+      FPart1 := count;
+
+    counts.Add(count);
+    if gcd = 0 then
+      gcd := count;
+    gcd := TNumberTheory.GreatestCommonDivisor(gcd, count);
   end;
+
+  for count in counts do
+  begin
+    if FPart2 = 0 then
+      FPart2 := count
+    else
+      FPart2 := count div gcd * FPart2;
+  end;
+
+  counts.Free;
+end;
+
+procedure THauntedWasteland.IncDirectionIndex;
+begin
+  Inc(FNextDirectionIndex);
+  if FNextDirectionIndex > Length(FDirections) then
+    FNextDirectionIndex := 1;
 end;
 
 constructor THauntedWasteland.Create;
 begin
-  FNextDirectionIndex := 1;
   FNodes := TNodes.Create;
   FUnparsedNodes := TNodes.Create(False);
-  FCurrentNode := nil;
-  FTargetNode := nil;
+  FGhostCurrentNodes := TNodes.Create(False);
 end;
 
 destructor THauntedWasteland.Destroy;
 begin
   FNodes.Free;
   FUnparsedNodes.Free;
+  FGhostCurrentNodes.Free;
   inherited Destroy;
 end;
 
@@ -213,16 +234,13 @@ procedure THauntedWasteland.ProcessDataLine(const ALine: string);
 begin
   if FDirections = '' then
     FDirections := ALine
-  else if (ALine <> '') and ((FTargetNode = nil) or (FCurrentNode <> FTargetNode)) then
-  begin
+  else if ALine <> '' then
     ProcessNode(ALine);
-    DoSteps;
-  end;
 end;
 
 procedure THauntedWasteland.Finish;
 begin
-
+  DoSteps;
 end;
 
 function THauntedWasteland.GetDataFileName: string;
diff --git a/tests/UHauntedWastelandTestCases.pas b/tests/UHauntedWastelandTestCases.pas
index 01fa5ba..1712650 100644
--- a/tests/UHauntedWastelandTestCases.pas
+++ b/tests/UHauntedWastelandTestCases.pas
@@ -33,6 +33,7 @@ type
     function CreateSolver: ISolver; override;
   published
     procedure TestPart1;
+    procedure TestPart2;
   end;
 
   { THauntedWastelandExampleTestCase }
@@ -59,6 +60,21 @@ type
     procedure TestPart1;
   end;
 
+  { TExample3HauntedWasteland }
+
+  TExample3HauntedWasteland = class(THauntedWasteland)
+    function GetDataFileName: string; override;
+  end;
+
+  { THauntedWastelandExample3TestCase }
+
+  THauntedWastelandExample3TestCase = class(TExampleEngineBaseTest)
+  protected
+    function CreateSolver: ISolver; override;
+  published
+    procedure TestPart2;
+  end;
+
 implementation
 
 { THauntedWastelandFullDataTestCase }
@@ -73,6 +89,11 @@ begin
   AssertEquals(14257, FSolver.GetResultPart1);
 end;
 
+procedure THauntedWastelandFullDataTestCase.TestPart2;
+begin
+  AssertEquals(16187743689077, FSolver.GetResultPart2);
+end;
+
 { THauntedWastelandExampleTestCase }
 
 function THauntedWastelandExampleTestCase.CreateSolver: ISolver;
@@ -104,9 +125,29 @@ begin
   AssertEquals(6, FSolver.GetResultPart1);
 end;
 
+{ TExample3HauntedWasteland }
+
+function TExample3HauntedWasteland.GetDataFileName: string;
+begin
+  Result := 'haunted_wasteland3.txt';
+end;
+
+{ THauntedWastelandExample3TestCase }
+
+function THauntedWastelandExample3TestCase.CreateSolver: ISolver;
+begin
+  Result := TExample3HauntedWasteland.Create;
+end;
+
+procedure THauntedWastelandExample3TestCase.TestPart2;
+begin
+  AssertEquals(6, FSolver.GetResultPart2);
+end;
+
 initialization
 
   RegisterTest(THauntedWastelandFullDataTestCase);
   RegisterTest(THauntedWastelandExampleTestCase);
   RegisterTest(THauntedWastelandExample2TestCase);
+  RegisterTest(THauntedWastelandExample3TestCase);
 end.