How to use the stack in this algorithm?

Question

Delphi

I wrote an algorithm with Virtu recursion for the problem of 8 queens, but I encountered the stack for the first time, can you please tell me what needs to be replaced in the code so that it turns out to be an algorithm using the stack, and not recursion?

unit Unit1;

interface

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

const maxlen = 15;
//15 - 2279184  14-365596

type
ta=array[1..maxlen]of 0..maxlen;

  TForm1 = class(TForm)
    DrawGrid1: TDrawGrid;
    SpeedButton1: TSpeedButton;
    SpeedButton2: TSpeedButton;
    SpinEdit1: TSpinEdit;
    Label1: TLabel;
    Label2: TLabel;
    SpinEdit2: TSpinEdit;
    procedure Draw(var a:ta);
    procedure SpeedButton1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure BackTracking(k:integer;a:ta);
    procedure SpeedButton2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation
var a:ta;
t:cardinal;
exitclick:boolean;
co:cardinal;
curlen:integer;
showtime:cardinal;

{$R *.dfm}
procedure TForm1.Draw(var a:ta);
var i:integer;
begin
DrawGrid1.Canvas.Brush.Color:=clblue;
for i:=1 to curlen do with DrawGrid1 do
  Canvas.Ellipse(CellRect(i-1,a[i]-1));
end;

procedure TForm1.BackTracking(k:integer;a:ta);
var i,j:integer;
po:boolean;
b:ta;
begin
if exitclick then exit;

if k<curlen then
        begin
        for i:=1 to curlen do b[i]:=a[i];
        for i:=1 to curlen do
                begin
                po:=true;
                for j:=1 to k do
                        begin
                        if a[j]=i then po:=false;
                        if abs(a[j]-i)=abs(j-k-1) then po:=false;
                        end;
                if po then
                        begin
                        b[k+1]:=i;
                        BackTracking(k+1,b);
                        end;
                end;
        end else
        begin
        co:=co+1;
        Form1.Caption:=IntToStr(co);
        Form1.Draw(a);        

        t:=GetTickCount;
        repeat
                Application.ProcessMessages;
        until (GetTickCount-t)>showtime;
        DrawGrid1.Repaint;      
        end;
end;

procedure TForm1.SpeedButton1Click(Sender: TObject);
begin
co:=0;
exitclick:=false;
showtime:=SpinEdit2.Value;
curlen:=SpinEdit1.Value;
DrawGrid1.ColCount:=curlen;
DrawGrid1.RowCount:=curlen;
DrawGrid1.DefaultColWidth:=trunc( (DrawGrid1.Width-2*curlen)/curlen);
DrawGrid1.DefaultRowHeight:=trunc( (DrawGrid1.Height-2*curlen)/curlen);

backTracking(0,a);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
DrawGrid1.Canvas.Brush.Color:=clblue;
curlen:=8;
showtime:=300;
end;

procedure TForm1.SpeedButton2Click(Sender: TObject);
begin
exitclick:=true;
end;

end.

Answer 1

Recursion is the stack