Leetcode 543. Diameter of Binary Tree

Given the root of a binary tree, return the length of the diameter of the tree.

The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

The length of a path between two nodes is represented by the number of edges between them.

Example 1:

Input: root = [1,2,3,4,5]
Output: 3
Explanation: 3 is the length of the path [4,2,1,3] or [5,2,1,3].
Example 2:

Input: root = [1,2]
Output: 1

Constraints:

The number of nodes in the tree is in the range [1, 104].
-100 <= Node.val <= 100

---

use nonlocal

# 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:
        def dfs(root):
            nonlocal max_len
            if root == None:
                return 0
            l = dfs(root.left)
            r = dfs(root.right)
            max_len = max(max_len, l+r)
            return max(l,r)+1
 
        max_len = 0
        dfs(root)
        return max_len