Diameter of Binary Tree

Given a binary tree, you need to compute 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.

Example:
Given a binary tree

          1
         / \
        2   3
       / \
      4   5

Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

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

 /**
  * Definition for a binary tree node.
  * public class TreeNode {
  *     int val;
  *     TreeNode left;
  *     TreeNode right;
  *     TreeNode(int x) { val = x; }
  * }
  */
 class Solution {
     public int diameterOfBinaryTree(TreeNode root) {
         int[] globalMax = new int[];
         helper(root, globalMax);
         return globalMax[] -  <=  ?  : globalMax[] - ;
     }

     private int helper(TreeNode root, int[] globalMax) {
         if (root == null) return ;
         int leftMaxWithRoot = helper(root.left, globalMax);
         int leftRightWithRoot = helper(root.right, globalMax);

         int maxWithRoot = Math.max(leftMaxWithRoot, leftRightWithRoot) + ;
         globalMax[] = Math.max(globalMax[], leftMaxWithRoot + leftRightWithRoot + );
         return maxWithRoot;
     }
 }