Added solution for "Day 14: Parabolic Reflector Dish", part 1

solvers/UParabolicReflectorDish.pas

@@ -0,0 +1,161 @@
+{
+  Solutions to the Advent Of Code.
+  Copyright (C) 2023  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
+  Foundation, either version 3 of the License, or (at your option) any later
+  version.
+
+  This program is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  this program.  If not, see <http://www.gnu.org/licenses/>.
+}
+
+unit UParabolicReflectorDish;
+
+{$mode ObjFPC}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, Generics.Collections, USolver;
+
+const
+  CRoundRockChar = 'O';
+  CCubeRockChar = '#';
+
+type
+
+  { TRockPile }
+
+  TRockPile = class
+  private
+    FStart, FLength: Integer;
+  public
+    constructor Create(const AStart: Integer);
+    procedure AddRock;
+    function Any: Boolean;
+    procedure SetStart(const AStart: Integer);
+    function CalcWeight(const ALineCount: Integer): Integer;
+  end;
+
+  TRockPiles = specialize TObjectList<TRockPile>;
+
+  { TParabolicReflectorDish }
+
+  TParabolicReflectorDish = class(TSolver)
+  private
+    FLineIndex: Integer;
+    FActivePiles, FFinishedPiles: TRockPiles;
+  public
+    constructor Create;
+    destructor Destroy; override;
+    procedure ProcessDataLine(const ALine: string); override;
+    procedure Finish; override;
+    function GetDataFileName: string; override;
+    function GetPuzzleName: string; override;
+  end;
+
+implementation
+
+{ TRockPile }
+
+constructor TRockPile.Create(const AStart: Integer);
+begin
+  FStart := AStart;
+  FLength := 0;
+end;
+
+procedure TRockPile.AddRock;
+begin
+  Inc(FLength);
+end;
+
+function TRockPile.Any: Boolean;
+begin
+  Result := (FLength > 0);
+end;
+
+procedure TRockPile.SetStart(const AStart: Integer);
+begin
+  FStart := AStart;
+end;
+
+function TRockPile.CalcWeight(const ALineCount: Integer): Integer;
+begin
+  Result := (2 * (ALineCount - FStart) - FLength + 1) * FLength div 2;
+end;
+
+{ TParabolicReflectorDish }
+
+constructor TParabolicReflectorDish.Create;
+begin
+  FLineIndex := 0;
+  FActivePiles := TRockPiles.Create;
+  FFinishedPiles := TRockPiles.Create;
+end;
+
+destructor TParabolicReflectorDish.Destroy;
+begin
+  FActivePiles.Free;
+  FFinishedPiles.Free;
+  inherited Destroy;
+end;
+
+procedure TParabolicReflectorDish.ProcessDataLine(const ALine: string);
+var
+  i: Integer;
+begin
+  Inc(FLineIndex);
+
+  // Initializes the list of active piles, one per column.
+  if FActivePiles.Count = 0 then
+  begin
+    FActivePiles.Count := Length(ALine);
+    for i:= 0 to FActivePiles.Count - 1 do
+      FActivePiles[i] := TRockPile.Create(0);
+  end;
+
+  // Updates the active piles from the current line.
+  for i := 1 to Length(ALine) do
+  begin
+    case ALine[i] of
+      CRoundRockChar: FActivePiles[i - 1].AddRock;
+      CCubeRockChar:
+        if FActivePiles[i - 1].Any then
+        begin
+          FFinishedPiles.Add(FActivePiles.ExtractIndex(i - 1));
+          FActivePiles.Insert(i - 1, TRockPile.Create(FLineIndex));
+        end
+        else
+          FActivePiles[i - 1].SetStart(FLineIndex);
+    end;
+  end;
+end;
+
+procedure TParabolicReflectorDish.Finish;
+var
+  i: Integer;
+begin
+  for i := 0 to FFinishedPiles.Count - 1 do
+    Inc(FPart1, FFinishedPiles[i].CalcWeight(FLineIndex));
+  for i := 0 to FActivePiles.Count - 1 do
+    Inc(FPart1, FActivePiles[i].CalcWeight(FLineIndex));
+end;
+
+function TParabolicReflectorDish.GetDataFileName: string;
+begin
+  Result := 'parabolic_reflector_dish.txt';
+end;
+
+function TParabolicReflectorDish.GetPuzzleName: string;
+begin
+  Result := 'Day 14: Parabolic Reflector Dish';
+end;
+
+end.
+