fun odwiedz (i,odw,v, l) =
  let fun g [] = [] | g (h::t) = (odwiedz (h,odw,v,l); g t) in
    if (Array.sub (odw,i)) = 0 then
        (
          Array.update (odw,i,1);
          l := i::(!l);
          g (Vector.sub (v,i));
          []
        )
    else []
  end



fun dfs x =
  let val v = Vector.fromList x and i = ref 0 and n = length x  and l = ref [] and odw = Array.array (length x, 0)
  in
     while !i <> n do
        (
          odwiedz (!i,odw,v, l);
          i := !i + 1
        );
      rev (!l)
  end