求根节点到叶节点数字之和-二叉树129-python

没看答案。

# 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:
        res = 0

        def dfs(pre, root):
            nonlocal res
			
			# 遇到叶子节点，res更新
            if not root.left and not root.right:
                pre = pre * 10 + root.val
                res += pre
                return
            
            pre = pre * 10 + root.val

            if root.left: 
                dfs(pre, root.left)
            if root.right:
                dfs(pre, root.right)
        
        dfs(0, root)
        
        return res