Python 双向链表的实现

概念：什么是双向链表

双向链表也叫双链表，是链表的一种，它的每个数据结点中都有两个指针，分别指向直接后继和直接前驱。

所以，从双向链表中的任意一个结点开始，都可以很方便地访问它的前驱结点和后继结点。一般我们都构造双向循环链表。

 代码简单实现：

"""
author: zhao xian xin

不积跬步无以至千里

"""

#定义双向链表 每一个结点
class Node(object):

    def __init__(self, item):
        self.previous = None
        self.item = item
        self.next = None


# 定义链表
class TwoWayLinkList():
    """ 链表基本属性 """
    def __init__(self):
        self.hearder = None
        self.length = 0


    """ 头部插入 """
    def firstAdd(self, node):
        if self.hearder == None:
            self.hearder = node
        else:
            node.next = self.hearder
            self.hearder.previous = node
            self.hearder = node
        self.length += 1


    """ 尾部插入 """
    def tailAdd(self, node):
        if self.length == 0:
            self.firstAdd(node)
        else:
            currentNode = self.hearder
            for i in range(self.length - 1):
                currentNode = currentNode.next
            node.previous = currentNode
            currentNode.next = node
            self.length += 1


    """ 根据指定索引 插入 对应结点 """
    def indexInsert(self, index, node):
        assert index != 0 or index <= self.length, "超出索引"
        if index == 1:
            self.firstAdd(node)
        elif index == 2:
            node.next = self.hearder.next
            node.prevopus = self.hearder
            self.hearder.next = node
            self.length += 1
        elif index > self.length:
            self.tailAdd(node)
        else:
            currentNode = self.hearder
            for i in range(1, index - 1):
                currentNode = currentNode.next
            node.prevopus = currentNode
            node.next = currentNode.next
            currentNode.next.previous = node
            currentNode.next = node
            self.length += 1


    """ 根据指定位置 删除 结点"""
    def delNode(self, index):
        """  判断删除的索引是否在标准范围之中  """
        assert index != 0 or index <= self.length, "超出索引"
        if index == 1:
            self.hearder = self.hearder.next
            self.hearder.previous = None
        elif index == 2:
            self.hearder.next = self.hearder.next.next
            self.hearder.next.next.previous = self.hearder
        else:
            currentNode = self.hearder
            for i in range(1, index - 1):
                currentNode = currentNode.next
            currentNode.next = currentNode.next.next
        self.length -= 1

    """ 遍历节点"""
    def rangeNode(self):
        assert self.length != 0 , "链表为空"
        currentNode = self.hearder
        for i in range(self.length):
            element = currentNode.item
            currentNode = currentNode.next
            print(element, end=" ")


    """ 结点之间的排序  不许改变指针位置， 只需改变链表中元素位置 """
    def sortNode(self):
        pass
        """ 快速排序 """
        for i in range(self.length):
            currentNode = self.hearder
            for j in range(0, self.length - i - 1):
                if currentNode.item > currentNode.next.item:
                    mid = currentNode.item
                    currentNode.item = currentNode.next.item
                    currentNode.next.item = mid
                """ 别忘记 交换节点 """
                currentNode = currentNode.next

if __name__ == "__main__":
    node = Node(2)
    t = TwoWayLinkList()
    t.firstAdd(node)
    print(t.rangeNode())

    """ 尾部 插入元素 """
    t.tailAdd(Node(1))
    t.tailAdd(Node(4))
    print(t.rangeNode())

    """ 头部插入位置 """
    t.firstAdd(Node(3))
    print(t.rangeNode())

    """ 根据索引插入对应的位置 """
    t.indexInsert(6, Node(5))
    print(t.rangeNode())

    """ 根据指定位置 删除节点 """
    t.delNode(4)
    print(t.rangeNode())

    """ 节点之间的 排序 """
    t.sortNode()
    print("======排序======")
    print(t.rangeNode())