Problem 4: Has Cycle (0pts)

The Link class can represent lists with cycles. That is, a list may contain itself as a sublist. Implement has_cycle that returns whether its argument lnk, a Link instance, contains a cycle. Try to solve it with constant space! (i.e. no list, dict, set or any other container)

def has_cycle(lnk):
    """ Returns whether `lnk` has cycle.

    >>> lnk = Link(1, Link(2, Link(3)))
    >>> has_cycle(lnk)
    False
    >>> lnk.rest.rest.rest = lnk
    >>> has_cycle(lnk)
    True
    >>> lnk.rest.rest.rest = lnk.rest
    >>> has_cycle(lnk)
    True
    """
    "*** YOUR CODE HERE ***"