Maximum Difference Between Node and Ancestor

def maxAncestorDiff(root: TreeNode) -> int:
    if root is None:
        return 0

    def _maxAncestorDiff(root, curMin, curMax):
        if root is None:
            return curMax - curMin

        curMin = min(root.val, curMin)
        curMax = max(root.val, curMax)

        leftTree = _maxAncestorDiff(root.left, curMin, curMax)
        rightTree = _maxAncestorDiff(root.right, curMin, curMax)

        return max(leftTree, rightTree)

    return _maxAncestorDiff(root, root.val, root.val)