# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def findFrequentTreeSum(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        if not root: return []
        freqs = {}
        self.sum(root, freqs)
        m = max(freqs.values())
        return [ k for k, v in freqs.items() if v == m ]

    def sum(self, root, freqs):
        if not root: return 0
        sum = root.val + self.sum(root.left, freqs) + self.sum(root.right, freqs)
        freqs[sum] = freqs.get(sum, 0) + 1
        return sum