LC543. 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:
        max_diameter = [0]
 
        def dfs(root):
            if root is None:
                return 0
 
            l = dfs(root.left)
            r = dfs(root.right)
            
            max_diameter[0] = max(max_diameter[0], l + r)
            return max(l, r) + 1
 
        dfs(root)
        return max_diameter[0]

Complexity

Time: $O(n)$
Space: $O(n)$