binarytreemaximumpathsum.py

'''
A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them. A node can only appear in the sequence at most once. Note that the path does not need to pass through the root.

The path sum of a path is the sum of the node's values in the path.

Given the root of a binary tree, return the maximum path sum of any non-empty path.

'''

# 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:
    
    answer = -float("inf")
    
    def maxPathSum(self, root: Optional[TreeNode]) -> int:
        self.dfs(root)
        return self.answer
    
    def dfs(self,node):
        if node is None:
            return 0
        
        left = self.dfs(node.left) 
        right = self.dfs(node.right)
        
        left = max(left,0)
        right = max(right,0)
        
        self.answer = max(self.answer,node.val+left+right)
        
        return node.val + max(left,right)