题目：
题解：
python
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def rob(self, root: TreeNode) -> int:
def _rob(root):
if not root: return 0, 0 # 偷，不偷
left = _rob(root.left)
right = _rob(root.right)
# 偷当前节点, 则左右子树都不能偷
v1 = root.val + left[1] + right[1]
# 不偷当前节点, 则取左右子树中最大的值
v2 = max(left) + max(right)
return v1, v2
return max(_rob(root))