[LeetCode] Hard - 124 Binary Tree Maximum Path Sum

▶124 - Binary Tree Maximum Path Sum

▶문제

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.

 

▶예제

Input: root = [1,2,3]
Output: 6
Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6.

Input: root = [-10,9,20,null,null,15,7]
Output: 42
Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42.

 

▶풀이

# 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: Optional[TreeNode]) -> int:
        def check(root):
            if not root:
                return 0
            l = check(root.left)
            r = check(root.right)
            
            Max = max(max(l, r) + root.val, root.val)
            Max2 = max(Max, l + r + root.val)

            self.res = max(self.res, Max2)
            return Max


        self.res = -9999999
        check(root)
        return self.res