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:

    1
   / \
  2   3
 / \
4   5

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
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# 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 __init__(self):
        self.max_diameter = -1
    
    def longest_path(self, root: Optional[TreeNode]) -> int:
        if not root:
            return 0
        left_path = self.longest_path(root.left)
        right_path = self.longest_path(root.right)
        self.max_diameter = max(self.max_diameter, left_path + right_path)
        return max(left_path, right_path) + 1
    
    def diameterOfBinaryTree(self, root: Optional[TreeNode]) -> int:
        self.longest_path(root)
        return self.max_diameter