129. 求根节点到叶节点数字之和 (Python 实现)

题目：

示例 1：

示例 2：

代码：

# 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 sumNumbers(self, root: TreeNode) -> int:
        def dfs (root, res):
            if not root:
                return 0
            res = res*10 + root.val
            if not root.left and not root.right:
                return res
            else:
                return dfs(root.left, res) + dfs(root.right, res)
        return dfs(root, 0)