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Write sorting/search methods that can be re-used (Views: 100)

 Problem/Question/Abstract:I find that alot of developers that use sorting and search algorithms, taking the Quick Sort algorithm for an example, will reimplement it for every use.Answer:Sorting algorithms rarely depend on actual knowledge what they are sorting, and when we require an algorithm and implement it, why restrict the algorithm to a specific use, as the algorithm itself will never change. They are only dependent on an index of which they then need to compare and exchange the information that resides at those indexes. The quick sort algorithm for the example would require only 3 main factors of which could be passed to a quick sort method. Start and End indexes Method for Comparing points Method for Exchanging points This going to apply for practially all sorting/searching algorithms. All that is required is that we specify the types that will define the Compare and Exchange methods. type  TIndexCompare = function(const ixA, ixB: integer): integer of object;  TIndexExchange = procedure(const ixA, ixB: integer) of object;  //-- Also these methods could be also reused for multiple sort algorythms.  //-- e.g  //-- procedure InsertionSortByIndex(ixLo, ixHi: Integer;  //--                                IndexCompare: TIndexCompare;  //--                                IndexExchange: TIndexExchange);  //--  etc....procedure QuickSortByIndex(ixLo, ixHi: Integer;  IndexCompare: TIndexCompare;  IndexExchange: TIndexExchange);implementationprocedure QuickSortByIndex(ixLo, ixHi: Integer;  IndexCompare: TIndexCompare;  IndexExchange: TIndexExchange);  procedure SortIndex(aLo, aHi: Integer);  var    I, J, P: Integer;    tmpInt: Integer;  begin    repeat      I := aLo;      J := aHi;      P := (aLo + aHi) shr 1;      repeat        while (I < aHi) and (IndexCompare(I, P) < 0) do          Inc(I);        while (J > aLo) and (IndexCompare(J, P) > 0) do          Dec(J);        if I <= J then        begin          IndexExchange(I, J);          if P = I then            P := J          else if P = J then            P := I;          Inc(i);          Dec(j);        end;      until I > J;      if aLo < J then        SortIndex(aLo, J);      aLo := I;    until I >= aHi;  end;begin  SortIndex(ixLo, ixHi);end;Now to use this..lets say i want to sort a listbox for the example(rather than using  the Listbox standard sorting)type  TMyForm = class(TForm)  private    ListBox1: TListBox;    btnSort: TButton;    .....    public    function IndexCompare(const ixA, ixB: integer): integer;    procedure IndexExchange(const ixA, ixB: integer);  end;  ..implementationfunction TMyForm.IndexCompare(const ixA, ixB: integer): integer;//-- Source to compare items.begin  Result := AnsiCompareText(ListBox1.Items[ixA], ListBox1.items[ixB]);end;procedure TMyForm.IndexExchange(const ixA, ixB: integer);// -- Source to exchange items.var  tmpStr: string;begin  tmpStr := ListBox1.Items[ixA];  ListBox1.Items[ixA] := ListBox1.Items[ixB];  ListBox1.Items[ixB] := tmpStr;end;procedure TMyForm.btnSortClick(Sender: TObject);begin  with ListBox1.items do  begin    BeginUpdate;    try      if UseQuickSort then        QuickSortByIndex(0, count - 1, IndexCompare, IndexExchange)      else        InsertionSortByIndex(0, count - 1, IndexCompare, IndexExchange);    finally      EndUpdate;    end;  end;end;//----Well hopefully that might of been some use Later All

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