543_diameter-of-binary-tree.py

# https://leetcode.com/problems/diameter-of-binary-tree/

# 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 diameterOfBinaryTree(self, root: Optional[TreeNode]) -> int:
        res = 0
        
        def dfs(root):
            if root is None:
                return 0

            l = dfs(root.left)
            r = dfs(root.right)
            
            nonlocal res
            res = max(res, l + r)
            
            return max(l, r) + 1
        
        dfs(root)
        return res