1. # Definition for a binary tree node.
    2. # class TreeNode:
    3. #     def __init__(self, x):
    4. #         self.val = x
    5. #         self.left = None
    6. #         self.right = None
    8. class Solution:
    9.     def hasPathSum(self, root: TreeNode, sum: int) -> bool:
    10.         # 自顶向下
    11.         def dfs(root, cusum):
    12.             if root is None:
    13.                 return False
    14.             if root.left is None and root.right is None:
    15.                 return cusum + root.val == sum
    17.             return dfs(root.left, cusum+root.val) or dfs(root.right, cusum+root.val)
    19.         return dfs(root, cusum=0) if root else False