我正在处理Leetcode问题“设计链接列表”，并且在使我的addAtIndex部分无法正常工作方面遇到问题。有人可以看一眼，然后告诉我我在做什么错吗？
class node(object):
def __init__(self, data=None):
self.next = None
self.data = data
class MyLinkedList(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self.head = node()
def get(self, index):
"""
Get the value of the index-th node in the linked list. If the index is invalid, return -1.
:type index: int
:rtype: int
"""
if index >= self.getLength():
return -1
cur = self.head
curIndex = 0
while True:
cur = cur.next
if curIndex == index:
return cur.data
curIndex += 1
def getLength(self):
cur = self.head
total = 0
while cur.next != None:
total += 1
cur=cur.next
return total
def addAtHead(self, val):
"""
Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.
:type val: int
:rtype: None
"""
first = node(val)
first.next = self.head
self.head = first
def addAtTail(self, val):
"""
Append a node of value val to the last element of the linked list.
:type val: int
:rtype: None
"""
last = node(val)
cur = self.head
while cur.next != None:
cur = cur.next
cur.next = last
def addAtIndex(self, index, val):
"""
Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted.
:type index: int
:type val: int
:rtype: None
"""
newNode = node(val)
cur = self.head
curIndex = 0
prev = None
if index == self.getLength()-1:
return self.addAtTail(val)
elif index >= self.getLength():
return
if index == 0:
newNode.next = self.head
self.head = newNode
else:
while curIndex < index:
prev = cur
cur = cur.next
curIndex = curIndex+1
newNode.next = prev.next
prev.next = newNode
cur = newNode
def deleteAtIndex(self, index):
"""
Delete the index-th node in the linked list, if the index is valid.
:type index: int
:rtype: None
"""
#if it's not the head or tail node
cur = self.head
curIndex = 0
if (cur.next!= None) and (self.head != None) and (index != 0):
while (cur.next != None):
if curIndex == index-1:
cur.next = (cur.next).next
curIndex += 1
cur = cur.next
#if it's the head node
elif index == 0:
temp = self.head
self.head = temp.next
#if it's the tail node
else:
temp = self.head
while temp.next != None:
prev = temp
temp = temp.next
prev.next = None
我希望输出[“ MyLinkedList”，“ addAtHead”，“ addAtTail”，“ addAtIndex”，“ get”，“ deleteAtIndex”，“ get”] [[]，[1]，[3]，[1,2]，[1]，[1]，[1]] 成为 [null，null，null，null，2，null，3]， 但我不断 [null，null，null，null，3，null，2]。
我做错了什么？