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procedure TForm148.Button1Click(Sender: TObject);

  procedure CountOccurrences(const List1, List2: TStrings; var Result: TStrings);
  var
    i, CurIndex: Integer;
  begin
    for i := 0 to List1.Count - 1 do
      Result.AddObject(List1[i], TObject(0));
    for i := 0 to List2.Count - 1 do
    begin
      CurIndex := Result.IndexOf(List2[i]);
      if CurIndex >= 0 then
        Result.Objects[CurIndex] := TObject(Succ(Integer(Result.Objects[CurIndex])));
    end;
  end;

var
  TempList: TStrings;
  i: Integer;
begin
  TempList := TStringList.Create;
  try
    CountOccurrences(ListBox1.Items, ListBox2.Items, TempList);
    for i := 0 to TempList.Count - 1 do
      ShowMessage(TempList[i] + ': ' + IntToStr(Integer(TempList.Objects[i])));
  finally
    TempList.Free;
  end;
end;					

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procedure TForm148.Button2Click(Sender: TObject);
type
  TIntArray = array of Integer;

  procedure CountOccurrences(const List1, List2: TStrings; var Result: TIntArray);
  var
    i, CurIndex: Integer;
  begin
    for i := 0 to List2.Count - 1 do
    begin
      CurIndex := List1.IndexOf(List2[i]);
      if CurIndex >= 0 then
        Result[CurIndex] := Succ(Result[CurIndex]);
    end;
  end;

var
  TempList: TIntArray;
  i: Integer;
begin
  SetLength(TempList, ListBox1.Items.Count);
  CountOccurrences(ListBox1.Items, ListBox2.Items, TempList);
  for i := Low(TempList) to High(TempList) do
    ShowMessage(ListBox1.Items[i] + ': ' + IntToStr(TempList[i]));
  SetLength(TempList, 0);
end;