我觉得是一样, 我改了下代码, 逻辑是一致的, 就是从数组->dict:

```python
def helper(self, root, sum):
from collections import defaultdict
if not root: return None

result = defaultdict(int)
result[root.val] += 1


left, right = self.helper(root.left, sum), self.helper(root.right, sum)

if left:
for key in left:
result[key+root.val] += left[key]
if right:
for key in right:
result[key+root.val] += right[key]

self.count += result[sum]

return result
```

不过不知怎么, 速度更慢了