Lab2_2

var a: array of integer := (20, 18, 7, 4, 5, 14, 6, 1, 12, 9);

procedure Partition (L,R: integer);
var
  i, j: integer;
  w, x: integer;
begin
  if L = R then Exit;
  i := L; j := R;
  x := a[(L + R) div 2 - 1];
  repeat
    while a[i - 1] < x do i := i + 1;
    while a[j - 1] > x do j := j - 1;
    if i <= j then
    begin
      w := a[i - 1]; a[i - 1] := a[j - 1]; a[j - 1] := w;
      i := i + 1; j := j - 1;
    end;
  until i > j;
  if L < j then Partition(L, j);
  if i < R then Partition(i, R);
end;


begin
  writeln(a);
  Partition(1, a.Length);
  writeln(a);
end.