test1111

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