129. Sum Root to Leaf Numbers - LeetCode Solution

# 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, n):

            
            if not root:
                return 0
            
            n = n*10
            n += root.val
            
            
            
            if  not root.left and not root.right:
                return n
                
            else:
                return dfs(root.left, n) + dfs(root.right, n)
                
            
        return dfs(root, 0)