# Definition for a binary tree node.
# class TreeNode(object):
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution(object):
# p.left = parent.right
# parent.right = p.right
# p.right = parent
# parent = p.left
# p = left
def upsideDownBinaryTree(self, root):
"""
:type root: TreeNode
:rtype: TreeNode
"""
# top-down
node, parent, parentRight = root, None, None
while node is not None:
left = node.left
node.left = parentRight
parentRight = node.right
node.right = parent
parent = node
node = left
return parent
