1. # Definition for a binary tree node.
    2. # class TreeNode:
    3. #     def __init__(self, val=0, left=None, right=None):
    4. #         self.val = val
    5. #         self.left = left
    6. #         self.right = right
    7. class Solution:
    8.     def maxPathSum(self, root: TreeNode) -> int:
    9.         return self.maxPathhelper(root)[1]
    12.     def maxPathhelper(self, root):
    13.         if root == None:
    14.             return 0, float('-inf')
    15.         left = self.maxPathhelper(root.left)
    16.         right = self.maxPathhelper(root.right)
    17.         singlePath = max(left[0], right[0]) + root.val
    18.         singlePath = max(singlePath, 0) #important line!!!
    19.         maxPath = max(left[1], right[1], left[0] + right[0] + root.val)
    20.         return singlePath, maxPath