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[12/11] 124. Binary Tree Maximum Path Sum

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작성일 2022.12.12 14:37

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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.

Example 1:

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

Example 2:

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.

Constraints:

The number of nodes in the tree is in the range [1, 3 * 104].
-1000 <= Node.val <= 1000

Accepted

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링크

https://leetcode.com/problems/binary-tree-maximum-path-sum/ 1677 회 연결

익명
작성일 2022.12.12 14:37

# 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:
        max_path = float('-inf')

        def dfs(node):
            if not node: return 0
            nonlocal max_path

            left = dfs(node.left)
            right = dfs(node.right)

            max_path = max(max_path, node.val+right + left, node.val+left, node.val+right, node.val)

            return max(node.val + right, node.val + left, node.val)
        
        dfs(root)
        return max_path