1602. Find Nearest Right Node in Binary Tree

# 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:
    def findNearestRightNode(self, root: TreeNode, u: TreeNode) -> Optional[TreeNode]:
        def dfs(root, i):
            nonlocal d, res
            if root is None or res:
                return
            if d == i:
                res = root
                return
            if root == u:
                d = i
                return
            dfs(root.left, i + 1)
            dfs(root.right, i + 1)

        d = 0
        res = None
        dfs(root, 1)
        return res