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Binary Tree Maximum Path Sum

Question​

What is the maximum possible sum of values from a root node to any leaf node in a binary tree?

Example 1
Input: [-10,9,20,null,null,15,7]
Output: 42

Solution​

all//Binary Tree Maximum Path Sum.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 maxPathSum(self, root):
        self.ans = float('-inf')

        def util(node):
            if not node:
                return 0

            left = max(util(node.left), 0)
            right = max(util(node.right), 0)

            self.ans = max(self.ans, node.val + left + right)

            return max(left, right) + node.val

        util(root)
        return self.ans