将值插入给定索引处的链接

Question

鉴于课程链接，

class Link:

    """A linked list.

    >>> s = Link(1, Link(2, Link(3, Link(4))))
    >>> len(s)
    4
    >>> s[2]
    3
    >>> s
    Link(1, Link(2, Link(3, Link(4))))
    """
    empty = ()

    def __init__(self, first, rest=empty):
        self.first = first
        self.rest = rest

    def __getitem__(self, i):
        if i == 0:
            return self.first
        else:
            return self.rest[i-1]

    def __len__(self):
        return 1 + len(self.rest)

    def __repr__(self):
        if self.rest:
            rest_str = ', ' + repr(self.rest)
        else:
            rest_str = ''
        return 'Link({0}{1})'.format(self.first, rest_str)

我该怎么写这个函数？

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

        >>> link = Link(1, Link(2, Link(3)))
        >>> insert(link, 9001, 0)
        >>> link
        Link(9001, Link(1, Link(2, Link(3))))
        >>> insert(link, 100, 2)
        >>> link
        Link(9001, Link(1, Link(100, Link(2, Link(3)))))
        >>> insert(link, 4, 5)
        Index out of bounds
        """
        "*** YOUR CODE HERE ***"

Answer 1

请查看以下内容：

class Link:
    empty = ()
    def __init__(self, first, rest=empty):
        self.first = first
        self.rest = rest

    def __getitem__(self, i):
        if i == 0:
            return self.first
        else:
            return self.rest[i-1]

    def __len__(self):
        return 1 + len(self.rest)

    def __repr__(self):
        if self.rest:
            rest_str = ', ' + repr(self.rest)
        else:
            rest_str = ''
        return 'Link({0}{1})'.format(self.first, rest_str)

def insert(link, value, index):
    if index >= link.__len__():
        print "Index out of bounds"
    else:
        if index == 0:
            tmp = link.first
            link.first = value
            link.rest = Link(tmp, link.rest)
        else:
            insert(link.rest, value, index - 1)

a = Link(1, Link(2, Link(3, Link(4))))
print a
insert(a,23,0)
print a
insert(a,12,2)
print a
insert(a,3,6)
print a
insert(a,3,5)
print a