Inserting items onto a sorted linked list, popping items off the list, and destroying the list...

http://www.awitness.org/delphi_pascal_tutorial/source/sorted_linked_list_insert_pop_dispose.html


unit Unit1;

interface

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

type
    link=^node;
    node=record C:integer; s:string; nextlink:link end;
  TForm1 = class(TForm)
    Memo1: TMemo;
    Edit1: TEdit;
    Edit2:TEdit;
    InsertButton: TButton;
    PopButton: TButton;
    DestroyButton: TButton;
    Procedure PopSortedStack(cpop:integer);
    procedure InsertButtonClick(Sender: TObject);
    procedure PopButtonClick(Sender: TObject);
    function SortedLinkedListInsert(cnew:integer; head:link):link;
    procedure FormCreate(Sender: TObject);
    procedure DestroyStack(ptr:link);
    procedure DestroyButtonClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  head, linkpoint:link;
implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
new(head); head^.C:=-1; head^.nextlink:=nil;

end;


Procedure TForm1.PopSortedStack(cpop:integer);
var temp, temp2:link;
begin
temp:=head;
if temp^.nextlink<>nil then begin
   while temp^.nextlink^.C<>cpop do temp:=temp^.nextlink;
   temp2:=temp^.nextlink^.nextlink;
   dispose(temp^.nextlink); temp^.nextlink:=temp2;
end;
{the following code is for visual testing of the code above}
temp2:=head;  Memo1.clear;
while temp2<>nil do begin
Memo1.Lines.Append(InttoStr(temp2^.C));
temp2:=temp2^.nextlink;
 end;
end;

procedure TForm1.DestroyStack(ptr:link);
begin

if ptr<>nil then begin
   if ptr^.nextlink<>nil then DestroyStack(ptr^.nextlink);
   dispose(ptr);
end;
end;


procedure TForm1.InsertButtonClick(Sender: TObject);
var
temp:link;
begin
temp:=SortedLinkedListInsert(StrToInt(Edit1.Text), head); {temp is only needed if you have
                                               additional fields in the record to fill}
temp^.s:=Edit2.Text; {enter the data into the fields of the record}

{the following code is test code for the list insert routine}
temp:=head; Memo1.Clear;
While temp<>nil do begin

      Memo1.Lines.Append(IntToStr(temp^.C));
      temp:=temp^.nextlink;
end;
end;

procedure TForm1.PopButtonClick(Sender: TObject);
begin
PopSortedStack(StrToInt(Edit1.Text));
end;


function TForm1.SortedLinkedListInsert(cnew:integer; head:link):link;
var Previous:link;  found:boolean;
begin
     found:=false;   Previous:=nil;
     repeat
           If cnew <= head^.C then found:=true;
           If (cnew > head^.C)  then begin
              Previous:=Head;
              head:=head^.nextlink;
           end;
     until (found) or (head=nil);
     new(linkpoint);
     linkpoint^.C := cnew;
     Linkpoint^.nextlink:=Previous^.nextlink;
     Previous^.nextlink:=linkpoint;
     Result:=Linkpoint;
end;

{This code rejects duplicate entries on the linked list


function TForm1.SortedLinkedListInsert(cnew:integer; head:link):link;
var Previous:link;  found, dupe:boolean;
begin
     found:=false;  dupe := false; Previous:=nil;
     result := nil;
     repeat
           If cnew < head^.C then found:=true;
           If cnew = head^.c then dupe := true;
           If (cnew > head^.C)  then begin
              Previous:=Head;
              head:=head^.nextlink;
           end;
     until (found) or (head=nil) or (dupe);
     If not dupe then begin
        new(linkpoint);
        linkpoint^.C := cnew;
        Linkpoint^.nextlink:=Previous^.nextlink;
        Previous^.nextlink:=linkpoint;
        Result:=Linkpoint;
     end;
   {  else  
         MessageDlg('that was a dupe', mterror, [mbok],0);     }

{end;


}

procedure TForm1.DestroyButtonClick(Sender: TObject);
var
temp:link;
begin
DestroyStack(head^.nextlink);
head^.nextlink:=nil;
Memo1.Clear; temp:=head;
While temp<>nil do begin

      Memo1.Lines.Append(IntToStr(temp^.C));
      temp:=temp^.nextlink;
end;
end;

end.