Added solution for "Day 16: The Floor Will Be Lava", part 2

solvers/UFloorWillBeLava.pas

@@ -42,14 +42,27 @@ type
     EnergyChange: TEnergyState;
   end;
 
+  { TEnergyMap }
+
+  TEnergyMap = class
+  private
+    FWidth, FHeight: Integer;
+    FStates: array of array of TEnergyState;
+  public
+    constructor Create(const AWidth, AHeight: Integer);
+    function IsBeamOutOfBounds(constref ABeam: TBeam): Boolean;
+    function Energize(constref APosition: TPoint; const AChange: TEnergyState): Boolean;
+    function CalcEnergizedTiles: Int64;
+  end;
+
   { TFloorWillBeLava }
 
   TFloorWillBeLava = class(TSolver)
   private
     FLines: TStringList;
-    function IsBeamOutOfBounds(constref ABeam: TBeam; const AWidth, AHeight: Integer): Boolean;
     function GetTile(constref APosition: TPoint): Char;
     function GetNewBeam(constref APosition, ADirection: TPoint): TBeam;
+    function ProcessBeam(ABeam: TBeam): Int64;
   public
     constructor Create;
     destructor Destroy; override;
@@ -62,7 +75,6 @@ type
 const
   CNoDirection: TPoint = (X: 0; Y: 0);
   CEmptyChar = '.';
-  CStartingBeam: TBeam = (Position: (X: 0; Y: 0); Direction: (X: 1; Y: 0));
   CTransitions: array of TTransition = (
     (IncomingDirection: (X: 1; Y: 0); OutgoingDirection: (X: 0; Y: -1); SplitDirection: (X: 0; Y: 0); Tile: '/';
       EnergyChange: esWestOrHorizontal),
@@ -92,14 +104,58 @@ const
 
 implementation
 
-{ TFloorWillBeLava }
+{ TEnergyMap }
 
-function TFloorWillBeLava.IsBeamOutOfBounds(constref ABeam: TBeam; const AWidth, AHeight: Integer): Boolean;
+constructor TEnergyMap.Create(const AWidth, AHeight: Integer);
+var
+  i, j: Integer;
 begin
-  Result := (ABeam.Position.X < 0) or (ABeam.Position.X >= AWidth)
+  FWidth := AWidth;
-    or (ABeam.Position.Y < 0) or (ABeam.Position.Y >= AHeight);
+  FHeight := AHeight;
+  SetLength(FStates, FWidth, FHeight);
+  for i := 0 to FWidth - 1 do
+    for j := 0 to FHeight - 1 do
+      FStates[i, j] := esNone;
 end;
 
+function TEnergyMap.IsBeamOutOfBounds(constref ABeam: TBeam): Boolean;
+begin
+  Result := (ABeam.Position.X < 0) or (ABeam.Position.X >= FWidth)
+    or (ABeam.Position.Y < 0) or (ABeam.Position.Y >= FHeight);
+end;
+
+function TEnergyMap.Energize(constref APosition: TPoint; const AChange: TEnergyState): Boolean;
+begin
+  Result := False;
+  case FStates[APosition.X, APosition.Y] of
+    esNone: FStates[APosition.X, APosition.Y] := AChange;
+    esWestOrHorizontal:
+      if AChange = esEastOrVertical then
+        FStates[APosition.X, APosition.Y] := esBoth
+      else
+        Result := True;
+    esEastOrVertical:
+      if AChange = esWestOrHorizontal then
+        FStates[APosition.X, APosition.Y] := esBoth
+      else
+        Result := True;
+    esBoth: Result := True;
+  end;
+end;
+
+function TEnergyMap.CalcEnergizedTiles: Int64;
+var
+  i, j: Integer;
+begin
+  Result := 0;
+  for i := 0 to FWidth - 1 do
+    for j := 0 to FHeight - 1 do
+      if FStates[i, j] <> esNone then
+        Inc(Result);
+end;
+
+{ TFloorWillBeLava }
+
 function TFloorWillBeLava.GetTile(constref APosition: TPoint): Char;
 begin
   Result := FLines[APosition.Y][APosition.X + 1];
@@ -111,6 +167,62 @@ begin
   Result.Direction := ADirection;
 end;
 
+function TFloorWillBeLava.ProcessBeam(ABeam: TBeam): Int64;
+var
+  done: Boolean;
+  energyMap: TEnergyMap;
+  stack: specialize TStack<TBeam>;
+  transition: TTransition;
+  energyChange: TEnergyState;
+begin
+  done := False;
+  energyMap := TEnergyMap.Create(Length(FLines[0]), FLines.Count);
+  stack := specialize TStack<TBeam>.Create;
+
+  repeat
+    // Processes the current beam.
+    if energyMap.IsBeamOutOfBounds(ABeam) then
+      done := True
+    else begin
+      if ABeam.Direction.X <> 0 then
+        energyChange := esWestOrHorizontal
+      else
+        energyChange := esEastOrVertical;
+
+      if GetTile(ABeam.Position) <> CEmptyChar then
+      begin
+        // Checks the current position for direction changes and splits.
+        for transition in CTransitions do
+          if (transition.IncomingDirection = ABeam.Direction) and (transition.Tile = GetTile(ABeam.Position)) then
+          begin
+            if transition.SplitDirection <> CNoDirection then
+              stack.Push(GetNewBeam(ABeam.Position + transition.SplitDirection, transition.SplitDirection));
+            ABeam.Direction := transition.OutgoingDirection;
+            energyChange := transition.EnergyChange;
+            Break;
+          end;
+      end;
+
+      done := energyMap.Energize(ABeam.Position, energyChange);
+
+      // Moves the beam.
+      ABeam.Position := ABeam.Position + ABeam.Direction;
+    end;
+
+    if done and (stack.Count > 0) then
+    begin
+      // Starts the next beam that was split earlier.
+      done := False;
+      ABeam := stack.Pop;
+    end;
+  until done;
+
+  stack.Free;
+
+  Result := energyMap.CalcEnergizedTiles;
+  energyMap.Free;
+end;
+
 constructor TFloorWillBeLava.Create;
 begin
   FLines := TStringList.Create;
@@ -129,87 +241,30 @@ end;
 
 procedure TFloorWillBeLava.Finish;
 var
-  energyMap: array of array of TEnergyState;
+  i, x, y, width, height: Integer;
-  width, height, i, j: Integer;
-  done: Boolean;
-  stack: specialize TStack<TBeam>;
   beam: TBeam;
-  transition: TTransition;
+  count: Int64;
-  energyChange: TEnergyState;
-  s: string;
 begin
-  // Initializes energy map.
   width := Length(FLines[0]);
   height := FLines.Count;
-  SetLength(energyMap, width, height);
+  for y := 0 to 1 do
-  for i := 0 to width - 1 do
+    for x := 0 to 1 do
-    for j := 0 to height - 1 do
-      energyMap[i, j] := esNone;
-
-  // Starts beam.
-  done := False;
-  beam := CStartingBeam;
-  stack := specialize TStack<TBeam>.Create;
-
-  repeat
-    // Processes the current beam.
-    if IsBeamOutOfBounds(beam, width, height) then
-      done := True
-    else begin
-      if beam.Direction.X <> 0 then
-        energyChange := esWestOrHorizontal
-      else
-        energyChange := esEastOrVertical;
-
-      if GetTile(beam.Position) <> CEmptyChar then
     begin
-        // Checks the current position for direction changes and splits.
+      // Direction is horizontal for y = 0, and vertical for y = 1.
-        for transition in CTransitions do
+      // Direction is positive for x = 0, and negative for x = 1.
-          if (transition.IncomingDirection = beam.Direction) and (transition.Tile = GetTile(beam.Position)) then
+      beam.Direction := Point((1 - 2 * x) * (1 - y), (1 - 2 * x) * y);
+      // Looping over the height for y = 0, and over the width for y = 1.
+      for i := 0 to height - 1 + (width - height) * y do
       begin
-            if transition.SplitDirection <> CNoDirection then
+        // Position is at left or top for x = 0, and right or bottom for x = 1.
-              stack.Push(GetNewBeam(beam.Position + transition.SplitDirection, transition.SplitDirection));
+        beam.Position := Point((x * (width - 1)) * (1 - y) + i * y, (x * (height - 1) - i) * y + i);
-            beam.Direction := transition.OutgoingDirection;
+        count := ProcessBeam(beam);
-            energyChange := transition.EnergyChange;
+        if FPart1 <= 0 then
-            Break;
+          FPart1 := count;
+        if FPart2 < count then
+          FPart2 := count;
       end;
     end;
-
-      // Energizes the current position.
-      case energyMap[beam.Position.X, beam.Position.Y] of
-        esNone: energyMap[beam.Position.X, beam.Position.Y] := energyChange;
-        esWestOrHorizontal:
-          if energyChange = esEastOrVertical then
-            energyMap[beam.Position.X, beam.Position.Y] := esBoth
-          else
-            done := True;
-        esEastOrVertical:
-          if energyChange = esWestOrHorizontal then
-            energyMap[beam.Position.X, beam.Position.Y] := esBoth
-          else
-            done := True;
-        esBoth: done := True;
-      end;
-
-      // Moves the beam.
-      beam.Position := beam.Position + beam.Direction;
-    end;
-
-    if done and (stack.Count > 0) then
-    begin
-      // Starts the next beam that was split earlier.
-      done := False;
-      beam := stack.Pop;
-    end;
-  until done;
-
-  stack.Free;
-
-  // Counts energized tiles.
-  for i := 0 to width - 1 do
-    for j := 0 to height - 1 do
-      if energyMap[i, j] <> esNone then
-        Inc(FPart1);
 end;
 
 function TFloorWillBeLava.GetDataFileName: string;

tests/UFloorWillBeLavaTestCases.pas

@@ -33,6 +33,7 @@ type
     function CreateSolver: ISolver; override;
   published
     procedure TestPart1;
+    procedure TestPart2;
   end;
 
   { TFloorWillBeLavaExampleTestCase }
@@ -42,6 +43,7 @@ type
     function CreateSolver: ISolver; override;
   published
     procedure TestPart1;
+    procedure TestPart2;
   end;
 
 implementation
@@ -58,6 +60,11 @@ begin
   AssertEquals(7392, FSolver.GetResultPart1);
 end;
 
+procedure TFloorWillBeLavaFullDataTestCase.TestPart2;
+begin
+  AssertEquals(7665, FSolver.GetResultPart2);
+end;
+
 { TFloorWillBeLavaExampleTestCase }
 
 function TFloorWillBeLavaExampleTestCase.CreateSolver: ISolver;
@@ -70,6 +77,11 @@ begin
   AssertEquals(46, FSolver.GetResultPart1);
 end;
 
+procedure TFloorWillBeLavaExampleTestCase.TestPart2;
+begin
+  AssertEquals(51, FSolver.GetResultPart2);
+end;
+
 initialization
 
   RegisterTest(TFloorWillBeLavaFullDataTestCase);