概念：什麼是雙向連結串列

雙向連結串列也叫雙鏈表，是連結串列的一種，它的每個資料結點中都有兩個指標，分別指向直接後繼和直接前驅。

所以，從雙向連結串列中的任意一個結點開始，都可以很方便地訪問它的前驅結點和後繼結點。一般我們都構造雙向迴圈連結串列。

程式碼簡單實現：

"""
author: zhao xian xin

不積跬步無以至千里

"""

#定義雙向連結串列 每一個結點
class Node(object):

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


# 定義連結串列
class TwoWayLinkList():
    """ 連結串列基本屬性 """
    def __init__(self):
        self.hearder = None
        self.length = 0


    """ 頭部插入 """
    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


    """ 根據指定索引 插入 對應結點 """
    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


    """ 根據指定位置 刪除 結點"""
    def delNode(self, index):
        """  判斷刪除的索引是否在標準範圍之中  """
        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

    """ 遍歷節點"""
    def rangeNode(self):
        assert self.length != 0 , "連結串列為空"
        currentNode = self.hearder
        for i in range(self.length):
            element = currentNode.item
            currentNode = currentNode.next
            print(element, end=" ")


    """ 結點之間的排序  不許改變指標位置， 只需改變連結串列中元素位置 """
    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
                """ 別忘記 交換節點 """
                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())

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

    """ 根據索引插入對應的位置 """
    t.indexInsert(6, Node(5))
    print(t.rangeNode())

    """ 根據指定位置 刪除節點 """
    t.delNode(4)
    print(t.rangeNode())

    """ 節點之間的 排序 """
    t.sortNode()
    print("======排序======")
    print(t.rangeNode())