双向链表

　　双向链表既可以向前，也可以向后，其节点是由两个指针域，一个指向上一个节点，一个指向下一个节点，和一个数据域构成的。第一个节点的指向前一个指针为None，最后一个节点指向下一个为None

　　代码实现：

# -*- coding = utf-8 -*-
# @Author: Wchime
# @time: 2023/1/20 20:34
# @file: 双向链表.py


class Nodes(object):
    """双向链表节点"""
    def __init__(self, item):
        self.item = item
        self.next = None
        self.prev = None


class DoubleLinkList(object):
    """
    双向链表
    """
    def __init__(self, node=None):
        self.__link = node

    def is_empty(self):
        # 链表是否为空
        return self.__link is None

    def get_length(self):
        """
        获取链表长度
        :return:
        """
        cur = self.__link
        count = 0
        while cur is not None:
            count += 1
            cur = cur.next
        return count

    def append(self,item):
        """
        添加节点, 当链表不是空链表时，需要找到最后一个节点
        :param item:
        :return:
        """
        node = Nodes(item)
        if self.is_empty():
            self.__link = node
        else:
            cur = self.__link
            while cur.next is not None:
                cur = cur.next
            cur.next = node
            node.prev = cur

    def insert(self, index, item):
        """
        在指定位置插入节点,插入在第n个时，需要将第m-n+1个元素向后移动位置
        :param index: 位置下标
        :param item: 插入值
        :return:
        """
        if index <=0:
            node = Nodes(item)
            node.next = self.__link
            self.__link = node
            node.next.prev = node
        elif index > self.get_length()-1:
            self.append(item)
        else:
            cur = self.__link
            count = 0
            while count < index:
                count += 1
                cur = cur.next
            node = Nodes(item)
            node.next = cur
            node.prev = cur.prev
            cur.prev.next = node
            cur.prev = node

    def remove(self, item):
        """
        根据值删除节点
        :param item:
        :return:
        """
        cur = self.__link
        while cur is not None:
            if cur.item == item:
                if cur == self.__link:
                    self.__link = cur.next
                    if cur.next:
                        # 判断链表是否只有一个节点
                        cur.next.prev = None
                else:
                    cur.prev.next = cur.next
                    if cur.next:
                        cur.next.prev = cur.prev
                break
            else:
                cur = cur.next

    def search(self, item):
        """
        查找节点是否存在
        :param item:
        :return:
        """
        cur = self.__link
        while cur is not None:
            if cur.item == item:
                return True
            else:
                cur = cur.next
        return False
    def travel(self):
        """
        链表遍历
        :return:
        """
        cur = self.__link
        while cur is not None:
            print(cur.item, end="  ")
            cur = cur.next
        print("")


if __name__ == "__main__":

    singlelist = DoubleLinkList()
    singlelist.append(1)
    singlelist.append(7)
    singlelist.append(5)
    singlelist.travel()

    singlelist.insert(1, 66)
    singlelist.travel()

    length = singlelist.get_length()
    print(length)

    print(singlelist.search(66))

    singlelist.remove(66)
    singlelist.travel()

    print(singlelist.is_empty())