## Sum root to leaf

Same as the last problem. We only want to add when there's no left or right node. State is kept by function.

```
from typing import Optional
# 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: Optional[TreeNode]) -> int:
return self.dfs(root, 0)
def dfs(self, node, currSum) -> int:
if node == None:
return 0
if node.left == None and node.right == None:
return int(str(currSum) + str(node.val))
else:
currSum = str(currSum) + str(node.val)
return self.dfs(node.left, currSum) + self.dfs(node.right, currSum)
```