题目
Given the root of a binary tree, return the sum of every tree node’s tilt.
The tilt of a tree node is the absolute difference between the sum of all left subtree node values and all right subtree node values. If a node does not have a left child, then the sum of the left subtree node values is treated as 0. The rule is similar if there the node does not have a right child.
解题思路
递归，对于每个节点，求出左右两个子树之和，将差的绝对值加到结果里，然后将两个子树之和加本身，返回给上一层
代码
class Solution:
def findTilt(self, root: TreeNode) -> int:
def dfs(root):
if not root:
return 0
left = dfs(root.left)
right = dfs(root.right)
self.res += abs(left - right)
return left + right + root.val
self.res = 0
dfs(root)
return self.res
