> For the complete documentation index, see [llms.txt](https://imhuay.gitbook.io/studies/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://imhuay.gitbook.io/studies/algorithms/problems/2022/07/leetcode0129-zhong-deng-qiu-gen-jie-dian-dao-ye-jie-dian-shu-zi-zhi-he.md).

# 求根节点到叶节点数字之和

![last modify](https://img.shields.io/static/v1?label=last%20modify\&message=2022-10-14%2014%3A59%3A33\&color=yellowgreen\&style=flat-square) [![](https://img.shields.io/static/v1?label=\&message=%E4%B8%AD%E7%AD%89\&color=yellow\&style=flat-square)](https://imhuay.gitbook.io/studies/algorithms/problems/2022/07/pages/R5NyOzkn3qAZy7wCx1pS#中等) [![](https://img.shields.io/static/v1?label=\&message=LeetCode\&color=green\&style=flat-square)](/studies/algorithms.md#leetcode) [![](https://img.shields.io/static/v1?label=\&message=%E4%BA%8C%E5%8F%89%E6%A0%91/%E6%A0%91\&color=blue\&style=flat-square)](https://imhuay.gitbook.io/studies/algorithms/problems/2022/07/pages/R5NyOzkn3qAZy7wCx1pS#二叉树树)

**问题简述**

```
给你一个二叉树的根节点 root ，树中每个节点都存放有一个 0 到 9 之间的数字。
每条从根节点到叶节点的路径都代表一个数字：

例如，从根节点到叶节点的路径 1 -> 2 -> 3 表示数字 123 。
计算从根节点到叶节点生成的 所有数字之和 。

叶节点 是指没有子节点的节点。
```

> [129. 求根节点到叶节点数字之和 - 力扣（LeetCode）](https://leetcode-cn.com/problems/sum-root-to-leaf-numbers/)

**思路：先序遍历**

* 先序遍历，每到一个叶节点，add 一次；
* 注意空节点的处理；

<details>

<summary><strong>Python</strong></summary>

```python
# 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:

        self.ret = 0

        def dfs(x, tmp):
            if not x:
                return

            tmp = tmp * 10 + x.val
            if not x.left and not x.right:
                self.ret += tmp
                return
            
            dfs(x.left, tmp)
            dfs(x.right, tmp)
        
        dfs(root, 0)
        return self.ret
```

</details>