543. 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 longestpath between any two nodes in a tree. This path may or may not pass through the root.

Example:
Given a binary tree

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

 1 public class Solution {
 2     int max = 0;
 3     
 4     public int diameterOfBinaryTree(TreeNode root) {
 5         maxDepth(root);
 6         return max;
 7     }
 8     
 9     private int maxDepth(TreeNode root) {
10         if (root == null) return 0;
11         
12         int left = maxDepth(root.left);
13         int right = maxDepth(root.right);
14         
15         max = Math.max(max, left + right);
16         
17         return Math.max(left, right) + 1;
18     }
19 }