code.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:

    def __init__(self) :
        self.maxVal = float('-inf')
    
    def maxPathSumInternal(self, root) :
        if not root :
            return float('-inf')
        elif not root.left and not root.right :
            self.maxVal = max(self.maxVal, root.val)
            return root.val
        
        left = self.maxPathSumInternal(root.left)
        right = self.maxPathSumInternal(root.right)

        if left>0 and right>0 :
            self.maxVal = max(self.maxVal, left, right, left+right+root.val)
        elif left>0 :
            self.maxVal = max(self.maxVal, left, left+root.val)
        elif right>0 :
            self.maxVal = max(self.maxVal, right, right+root.val)
        else :
            self.maxVal = max(self.maxVal, root.val)
        
        maVal = max(left, right)
        if maVal > 0 :
            return root.val+maVal
        else :
            return root.val

    def maxPathSum(self, root: Optional[TreeNode]) -> int:
        self.maxPathSumInternal(root)

        return self.maxVal