'''
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: 3is 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
'''
# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def diameterOfBinaryTree(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        result = 0

        def dfs_diameter(root):
        	if root is None:
        		return -1
        	left_height = dfs_diameter(root.left)
        	right_height = dfs_diameter(root.right)

        	result = max(result, 2 + left_height + right_height)
        	return 1 + max(left_height, right_height)

        dfs_diameter(root)
        return result