1.题目

2. 思想

递归

3. 代码

# 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 __init__(self):
        self.res = 0

    def sumNumbers(self, root: Optional[TreeNode]) -> int:
        self.dfs(root,tmp=0)
        return self.res
    
    # A deep search finds all leaf nodes
    # tmp Represents the value from the root node to the current node
    def dfs(self,root,tmp):
        if root is None: # 如果是None,Explanation is over
            return 
        
        if root.left:
            self.dfs(root.left,tmp*10 + root.val)
        if root.right:
            self.dfs(root.right,tmp*10 + root.val)

        # If left and right nodes are empty,Indicates that it is currently the root node
        if root.left ==None and root.right==None:
            self.res += (tmp*10 + root.val)