python双向链表的实现

　　python双向链表和单链表类似，只不过是增加了一个指向前面一个元素的指针,下面的代码实例了python双向链表的方法

示意图：

python双向链表实现代码：

# -*- coding: utf-8 -*-
class Node(object):
    def __init__(self, val, p=0):
        self.data = val
        self.next = p
        self.prev = p


class LinkList(object):
    def __init__(self):
        self.head = 0

    def __getitem__(self, key):

        if self.is_empty():
            print('linklist is empty.')
            return

        elif key < 0 or key > self.getlength():
            print('the given key is error')
            return

        else:
            return self.getitem(key)

    def __setitem__(self, key, value):

        if self.is_empty():
            print('linklist is empty.')
            return

        elif key < 0 or key > self.getlength():
            print('the given key is error')
            return

        else:
            self.delete(key)
            return self.insert(key)

    def initlist(self, data):

        self.head = Node(data[0])

        p = self.head

        for i in data[1:]:
            node = Node(i)
            p.next = node
            node.prev = p
            p = p.next

    def getlength(self):

        p = self.head
        length = 0
        while p != 0:
            length += 1
            p = p.next

        return length

    def is_empty(self):

        if self.getlength() == 0:
            return True
        else:
            return False

    def clear(self):

        self.head = 0

    def append(self, item):

        q = Node(item)
        if self.head == 0:
            self.head = q
        else:
            p = self.head
            while p.next != 0:
                p = p.next
            p.next = q
            q.prev = p

    def getitem(self, index):

        if self.is_empty():
            print('Linklist is empty.')
            return
        j = 0
        p = self.head

        while p.next != 0 and j < index:
            p = p.next
            j += 1

        if j == index:
            return p.data
        else:
            print('target is not exist!')

    def insert(self, index, item):

        if self.is_empty() or index < 0 or index > self.getlength():
            print('Linklist is empty.')
            return

        if index == 0:
            q = Node(item, self.head)

            self.head = q

        p = self.head
        post = self.head
        j = 0
        while p.next != 0 and j < index:
            post = p
            p = p.next
            j += 1

        if index == j:
            q = Node(item, p)
            post.next = q
            q.prev = post
            q.next = p
            p.prev = q

    def delete(self, index):

        if self.is_empty() or index < 0 or index > self.getlength():
            print('Linklist is empty.')
            return

        if index == 0:
            q = Node(item, self.head)

            self.head = q

        p = self.head
        post = self.head
        j = 0
        while p.next != 0 and j < index:
            post = p
            p = p.next
            j += 1

        if index == j:
            post.next = p.next
            p.next.prev = post

    def index(self, value):

        if self.is_empty():
            print('Linklist is empty.')
            return

        p = self.head
        i = 0
        while p.next != 0 and not p.data == value:
            p = p.next
            i += 1

        if p.data == value:
            return i
        else:
            return -1


l = LinkList()
l.initlist([1, 2, 3, 4, 5])
print(l.getitem(4))
l.append(6)
print(l.getitem(5))
l.insert(4, 40)
print(l.getitem(3))
print(l.getitem(4))
print(l.getitem(5))
l.delete(5)
print(l.getitem(5))
l.index(5)

输出：

5
6
4
40
5
6