[LeetCode] 543. Diameter of Binary Tree (Python)

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# Definition for a binary tree node.
from typing import Optional


class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


class Solution:
    def __init__(self):
        self.longest = 0

    def diameterOfBinaryTree(self, root: Optional[TreeNode]) -> int:
        def dfs(node: TreeNode) -> int:
            if not node:
                return -1

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

            self.longest = max(self.longest, left + right + 2)  # 거리

            return max(left, right) + 1  # 상태값

        dfs(root)

        return self.longest