def get_dir_from_zipfile(zip_file, fallback=None):
    """Return the name of the root folder in a zip file.

    :param zip_file: a :class:`zipfile.ZipFile` instance.
    :param fallback: if `None`, the name of the zip file is used. This is
        returned if the zip file contains more than one top-level directory,
        or none at all.
    """
    fallback = fallback or zip_file.filename
    directories = [name for name in zip_file.namelist() if name.endswith("/")
                   and len(PurePath(name).parts) == 1]
    return fallback if len(directories) > 1 else directories[0]
def test():
    start = time.time()
    treap = None
    s = set()
    for i in range(100000):
        key = random.randint(0, 10000)
        if random.randint(0, 1) == 0:
            if key in s:
                treap = remove(treap, key)
                s.remove(key)
        elif key not in s:
            treap = insert(treap, key)
            s.add(key)
        assert len(s) == size(treap)

    for i in range(size(treap)):
        assert kth(treap, i) in s
    print(time.time() - start)