""" Extra Questions for Lab 13 """

# Q4
def num_splits(s, d):
    """Return the number of ways in which s can be partitioned into two
    sublists that have sums within d of each other.

    >>> num_splits([1, 5, 4], 0)  # splits to [1, 4] and [5]
    1
    >>> num_splits([6, 1, 3], 1)  # no split possible
    0
    >>> num_splits([-2, 1, 3], 2) # [-2, 3], [1] and [-2, 1, 3], []
    2
    >>> num_splits([1, 4, 6, 8, 2, 9, 5], 3)
    12
    """
    "*** YOUR CODE HERE ***"

# Q5
def insert(link, value, index):
    """Insert a value into a Link at the given index.

    >>> link = Link(1, Link(2, Link(3)))
    >>> print(link)
    <1 2 3>
    >>> insert(link, 9001, 0)
    >>> print(link)
    <9001 1 2 3>
    >>> insert(link, 100, 2)
    >>> print(link)
    <9001 1 100 2 3>
    >>> insert(link, 4, 5)
    IndexError
    """
    "*** YOUR CODE HERE ***"

class Link:
    """A linked list.

    >>> s = Link(1)
    >>> s.first
    1
    >>> s.rest is Link.empty
    True
    >>> s = Link(2, Link(3, Link(4)))
    >>> s.second
    3
    >>> s.first = 5
    >>> s.second = 6
    >>> s.rest.rest = Link.empty
    >>> s                                    # Displays the contents of repr(s)
    Link(5, Link(6))
    >>> s.rest = Link(7, Link(Link(8, Link(9))))
    >>> s
    Link(5, Link(7, Link(Link(8, Link(9)))))
    >>> print(s)                             # Prints str(s)
    <5 7 <8 9>>
    """
    empty = ()

    def __init__(self, first, rest=empty):
        assert rest is Link.empty or isinstance(rest, Link)
        self.first = first
        self.rest = rest

    @property
    def second(self):
        return self.rest.first

    @second.setter
    def second(self, value):
        self.rest.first = value


    def __repr__(self):
        if self.rest is not Link.empty:
            rest_repr = ', ' + repr(self.rest)
        else:
            rest_repr = ''
        return 'Link(' + repr(self.first) + rest_repr + ')'

    def __str__(self):
        string = '<'
        while self.rest is not Link.empty:
            string += str(self.first) + ' '
            self = self.rest
        return string + str(self.first) + '>'

    def __len__(self):
        """ Return the number of items in the linked list.

        >>> s = Link(1, Link(2, Link(3)))
        >>> len(s)
        3
        >>> s = Link.empty
        >>> len(s)
        0
        """
        return 1 + len(self.rest)

    def __getitem__(self, i):
        """Returning the element found at index i.

        >>> s = Link(1, Link(2, Link(3)))
        >>> s[1]
        2
        >>> s[2]
        3
        """
        if i == 0:
            return self.first
        else:
            return self.rest[i-1]

    def __setitem__(self, index, element):
        """Sets the value at the given index to the element

        >>> s = Link(1, Link(2, Link(3)))
        >>> s[1] = 5
        >>> s
        Link(1, Link(5, Link(3)))
        >>> s[4] = 5
        Traceback (most recent call last):
        ...
        IndexError
        """
        if index == 0:
            self.first = element
        elif self.rest is Link.empty:
            raise IndexError
        else:
            self.rest[index - 1] = element

    def __contains__(self, e):
        return self.first == e or e in self.rest

    def map(self, f):
        self.first = f(self.first)
        if self.rest is not Link.empty:
            self.rest.map(f)