题目
| Given the root of a binary tree, find the maximum value V for which there exist different nodes A and B where V = | A.val - B.val | and A is an ancestor of B. |
A node A is an ancestor of B if either: any child of A is equal to B, or any child of A is an ancestor of B.
解题思路
递归，每次向下传递当前路径上的最大值和最小值（因为为了差最大，不会是中间的节点），然后与当前的值做差，更新结果
代码
class Solution:
def maxAncestorDiff(self, root: TreeNode) -> int:
def dfs(root, max_val, min_val):
tmp = max(abs(root.val - max_val), abs(root.val - min_val))
self.res = max(self.res, tmp)
max_val = max(max_val, root.val)
min_val = min(min_val, root.val)
if root.left:
dfs(root.left, max_val, min_val)
if root.right:
dfs(root.right, max_val, min_val)
self.res = 0
dfs(root, root.val, root.val)
return self.res
