test.ml

let partition a p =
  let len = Array.length a in
  let rec loop l r =
    if r = len then l
    else if p a.(r) then begin
      let tmp = a.(l) in
      a.(l) <- a.(r);
      a.(r) <- tmp;
      loop (l + 1) (r + 1)
    end else
      loop l (r + 1)
  in
  loop 0 0