双链表实现

核心思路

核心思路就是抽象为现实生活中的排队问题，如何在一个队列中插队、插入那个位置、队列的头时谁，尾时谁？不管是插入合适删除，遇到边界问题如何处理，代码要有健壮性。

代码实现

#-*- coding=UTF-8 -*-
import random
class Nodes:
    """no doc"""
    def __init__(self,value,previous=None,next=None):
        self.value = value
        self._next = next
        self._previous = previous

class LinkList:
    """no doc"""
    def __init__(self,head=None,tail=None):
        self.head = head
        self.tail = tail
        self._length = 0

    def __str__(self):
        string = str([x for x in self.iternodes()]).strip("[]")
        return "<{}>".format(string)

    def __len__(self):
        return self._length

    def append(self,value):
        """
        :param value: 添加的元素
        :return: None
        """
        node = Nodes(value)
        obj = self.head

        if self.head == None:
            self.head = node
            self.tail = node
            self._length += 1
        else:
            # 找最后一个元素
            while True:
                if obj._next != None:
                    obj = obj._next
                else:
                    #第一个元素的next属性指向新增node实例
                    obj._next = node
                    #新增实例的previous属性指向之前的实例
                    node._previous = obj
                    #每次新增元素，更新self.tail元素
                    self.tail = node
                    self._length += 1
                    break

    def pop(self):
        """no doc"""
        obj = self.head
        elementnum = 0
        index = random.randint(0,len(self)-1)

        while elementnum < index:
            obj = obj._next
            elementnum += 1

        #边界进行处理
        if obj._next == None : #随机是最后一个元素时的动作
            obj._previous._next = None
            self._length -= 1
        elif obj._previous == None: #随机是第一个元素时的动作
            obj._next._previous = None
            self.head = obj._next
            self._length -= 1
        else:
            obj._previous._next = obj._next
            obj._next._previous = obj._previous
            self._length -= 1

    def insert(self,index,value):
        """no doc insert"""
        obj = self.head
        elementnum = 0

        if index > len(self)-1:
            print("out of index")
            return "out of index"

        while elementnum < index-1:
            obj = obj._next
            elementnum += 1

        node = Nodes(value)
        #修改元素属性
        if index == 0: #边界处理，当插入位置为第一个位置时的动作
            self.head._previous = node
            node._next = self.head
            self.head = node
            self._length += 1
        else:
            obj._next._previous = node
            node._next =obj._next
            obj._next = node
            node._previous = obj
            self._length += 1

    def remove(self,value):
        """no doc"""
        obj = self.head

        while True:
            if obj.value != value:
                obj = obj._next
                continue
            elif obj.value == self.head.value:
                obj._next._previous = None
                self.head = obj._next
                self._length -= 1
                del obj
            elif obj.value == self.tail.value:
                obj._previous._next = None
                self.tail = obj._previous
                self._length -= 1
            else:
                #删除对象前一个元素的next指向下一个元素
                obj._previous._next = obj._next
                obj._next._previous = obj._previous
                self._length -= 1
                del obj
                break

    def iternodes(self):
        """
        从头开始跌代，不能回头
        :return: None
        """
        obj = self.head

        while True:
            if obj == None:
                break
            else:
                yield obj.value
                obj = obj._next

#测试代码
link = LinkList()
link.append(5)
link.append(6)
link.append(7)
link.append(8)
link.insert(3,10)
print(link)