# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right

class Solution:

    #TS: O(vertices)
    #SC: O(max depth)

    #V is taken as the difference between the maximum and minimum of a node with its children (includeing itself) on a SINGLE PATH
    #Thus recording the MIN and MAX from bottom to up is difficult to achieve.
    #Instead, recorder the MIN and MAX from up to bottom.    



    def maxAncestorDiff(self, root: TreeNode) -> int:

        self.res = 0
        self.helper(root, root.val, root.val)
        return self.res

    def helper(self, root, Min, Max):

        if not root:
            return

        Max = max(Max, root.val)
        Min = min(Min, root.val)

        self.res = max(self.res, Max - Min)

        self.helper(root.left, Min, Max)
        self.helper(root.right, Min, Max)