将节点都移到右边,每个节点本身作为下一个节点的前节点，本身又为上一节点的后节点
# 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):
def flatten(self, root):
"""
:type root: TreeNode
:rtype: void Do not return anything, modify root in-place instead.
"""
if not root:
return None
self.flatten(root.right)
self.flatten(root.left)
root.right = self.prev
root.left = None
self.prev = root
def __init__(self):
self.prev = None
