AdventOfCode2023/solvers/UParabolicReflectorDish.pas

{
  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.