【二叉树-困难】124. 二叉树中的最大路径和

【题目】
【代码】

# 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 visit(self,root):
        if not root:
            return 0
        l=max(self.visit(root.left),0)
        r=max(self.visit(root.right),0)
        self.cnt=max(self.cnt,l+r+root.val)
        # print(root.val," l:",l," r:",r)
        return root.val+max(l,r)
    def maxPathSum(self, root: Optional[TreeNode]) -> int:
        self.cnt=-30000000
        self.visit(root)        
        return self.cnt