参考的这个题解，其中注意python的变量是标签，给tail赋next的时候可能会影响到node
https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/discuss/37824/AC-Python-O(1)-space-solution-12-lines-and-easy-to-understand
"""
# Definition for a Node.
class Node:
def __init__(self, val: int = 0, left: 'Node' = None, right: 'Node' = None, next: 'Node' = None):
self.val = val
self.left = left
self.right = right
self.next = next
"""
class Solution:
def connect(self, root: 'Node') -> 'Node':
tail = dummy = Node(0)
node = root
while node:
tail.next = node.left
if tail.next:
tail = tail.next
tail.next = node.right
if tail.next:
tail = tail.next
node = node.next
if not node:
tail = dummy
node = dummy.next
return root
