leetcode-129-求根到叶子结点数字之和

题目描述：

第一次提交：

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

class Solution:
    def sumNumbers(self, root: TreeNode) -> int:
        if not root:
            return 0
        res = 0
        def helper(root,temp):
            nonlocal res
            if not root:
                return
            else:
                temp = temp*10 + root.val
                if not root.left and not root.right:
                    res += temp
            helper(root.left,temp)
            helper(root.right,temp)
                
        helper(root,0)
        return res