/**
  If you are looking for extra practice at implementing data structures, here's one additional exercise:

  Create an ArrayList class with an add(o) method (it doesn't have to grow the array -- we'll ignore that
  detail this time and just assume _underlyingStorage is always big enough). However, it should have an
  additional method:

  ArrayList<T> intersect (ArrayList<T> other)

  This method examines the contents of the "other" ArrayList, finds the elements that are contained both
  in "this" ArrayList *and* in "other", and then instantiates and returns a *third* ArrayList containing
  those elements. You may implement any other "helper" methods that you wish; you are only required to
  implement add(o) and intersect(other) methods.
*/
class ArrayList<T> {
  T[] _underlyingStorage;
  ...
  void add (T o) {
    ...
  }

  ArrayList<T> intersect (ArrayList<T> other) {
    ...
  }
}