Deque Duplamente Encadeado Alternado

unit UDeque;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, Buttons, StdCtrls, ExtCtrls;

type
  No = Record
    Valor: String[10];
    LE, LD: Pointer;
  end;
  TFDeque = class(TForm)
    EditValor: TEdit;
    Label1: TLabel;
    EditDeque: TEdit;
    Label2: TLabel;
    Panel1: TPanel;
    Button1: TButton;
    Button2: TButton;
    BitBtn1: TBitBtn;
    Memo1: TMemo;
    Memo2: TMemo;
    procedure FormShow(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure RGClick(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
    procedure MostraDeque;
    procedure InsereEsq;
    procedure InsereDir;
    procedure RetiraEsq;
    procedure RetiraDir;
  public
    { Public declarations }
  end;

var
  D, Aux: ^No;
  PDir, PEsq: Pointer;
  FDeque: TFDeque;
  LadoI: String[1];
  LadoR: String[1];
  X: integer;

implementation

{$R *.dfm}


procedure TFDeque.FormShow(Sender: TObject);
begin
  PDir := nil;
  PEsq := nil;
  LadoI := 'E';
  LadoR := 'E';
  X := 0;
end;

procedure TFDeque.Button1Click(Sender: TObject);
begin
  if EditValor.Text = '' then
  begin
    ShowMessage ('Valor inválido!');
    EditValor.SetFocus;
  end
  else
  begin
    try
      New(D);
    Except
      ShowMessage('Erro ao criar nó!');
      EditValor.Clear;
      EditValor.SetFocus;
      Exit;
    end;
    if LadoI = 'E' then
      InsereEsq
    else
      InsereDir;
  end;
end;

procedure TFDeque.InsereEsq;
begin
  D.Valor := EditValor.Text;
  if PEsq = nil then
  begin
    PEsq := D;
    PDir := D;
    D.LE := D;
    D.LD := D;
  end
  else
  begin
    Aux := PEsq;
    Aux.LE := D;
    D.LD := Aux;
    D.LE := PDir;
    PEsq := D;
    Aux := PDir;
    Aux.LD := PEsq;
  end;
  if X < 1 then
    Inc(X)
  else
  begin
    X := 0;
    LadoI := 'D';
  end;
  EditValor.Clear;
  EditValor.SetFocus;
  MostraDeque;
end;

procedure TFDeque.MostraDeque;
begin
  EditDeque.Text := '| ';
  Aux := PEsq;
  While Aux <> PDir do
  begin
    EditDeque.Text := EditDeque.Text + Aux.Valor + ' | ';
    Aux := Aux.LD;
  end;
  EditDeque.Text := EditDeque.Text + Aux.Valor + ' |';
end;

procedure TFDeque.InsereDir;
begin
  D.Valor := EditValor.Text;
  if PDir = nil then
  begin
    PDir := D;
    PEsq := D;
    D.LE := D;
    D.LD := D;
  end
  else
  begin
    D.LE := PDir;
    Aux := PDir;
    Aux.LD := D;
    PDir := D;
    Aux := D;
    Aux.LD := PEsq;
    Aux := PEsq;
    Aux.LE := PDir;
  end;
  if X < 1 then
    Inc(X)
  else
  begin
    X := 0;
    LadoI := 'E';
  end;
  EditValor.Clear;
  EditValor.SetFocus;
  MostraDeque;
end;


procedure TFDeque.RGClick(Sender: TObject);
begin
  EditValor.SetFocus;
end;

procedure TFDeque.Button2Click(Sender: TObject);
begin
  if PDir = nil then
  begin
    ShowMessage('Deque vazio!');
    EditValor.SetFocus;
  end
  else
  begin
    if PDir = PEsq then
    begin
      PDir := nil;
      PEsq := nil;
      EditDeque.Clear;
      EditValor.SetFocus;
    end
    else
    begin
      if LadoR = 'E' then
       RetiraEsq
      else
        RetiraDir;
    end;
  end;
end;

procedure TFDeque.RetiraEsq;
begin
  Aux := PEsq;
  Aux := Aux.LD;
  PEsq := nil;
  PEsq := Aux;
  Aux.LE := PDir;
  Aux := PDir;
  Aux.LD := PEsq;
  MostraDeque;
  LadoR := 'D';
end;

procedure TFDeque.RetiraDir;
begin
  Aux := PDir;
  Aux := Aux.LE;
  PDir := nil;
  PDir := Aux;
  Aux.LD := PEsq;
  Aux := PEsq;
  Aux.LE := PDir;
  MostraDeque;
  LadoR := 'E';
end;
end.