class Solution:
def findTilt(self, root: TreeNode) -> int:
self.res = 0
def postOrder(root):
if not root:
return 0
left = postOrder(root.left)
right = postOrder(root.right)
sum = left + right + root.val
root.val = abs(left-right)
self.res += root.val #累加坡度
return sum
postOrder(root)
return self.res
