Diameter of the 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.

Class TreeNode:
    val (int)
    left (TreeNode)
    right (TreeNode)

Input Format

First parameter - TreeNode root

Output Format

Return the number

Example 1:

Input : 
    root = [3 9 20 null null 15 7]
Output :
    3
Explanation :
    3 is the length of the path [7 20 3 9] or [15 20 3 9].

Example 2:

Input :
    root = [10 20]
Output :
    1

Constraints:

• The number of nodes in the tree is in the range [1, 10⁴].
• -100 <= Node.val <= 100
• Expected Time Complexity: O(N)
• Expected Space Complexity: O(N)