LeetCode_Sum Root to Leaf Numbers

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Sum Root to Leaf Numbers

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. An example is the root-to-leaf path 1->2->3 which represents the number 123. Find the total sum of all root-to-leaf numbers.
（树型数值之和）

Note: A leaf is a node with no children.

Example:



1. DFS

常规的 DFS 算法，具体实现过程如下：

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

class Solution:
    def dfs(self, root):
        if not root:
            return
        
        left = self.dfs(root.left)
        right = self.dfs(root.right)
        
        if not left and not right:
            return str(root.val)
        
        result = []
        if left:
            for num in left:
                result.append(str(root.val)+str(num)) 
        if right:
            for num in right:
                result.append(str(root.val)+str(num))
        
        return result
        
    def sumNumbers(self, root: TreeNode) -> int:
        if not root:
            return 0
        
        nums = self.dfs(root)
        return  sum(int(num) for num in nums)