题目：

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.

链接：https://leetcode.com/problems/diameter-of-binary-tree/#/description

4/1/2017

10ms

 1 public class Solution {
 2     int maxDiff = 0;
 3     public int diameterOfBinaryTree(TreeNode root) {
 4         heightOfBinaryTree(root);
 5         return maxDiff;
 6     }
 7     private int heightOfBinaryTree(TreeNode root) {
 8         if (root == null) return 0;
 9         int heightL = heightOfBinaryTree(root.left);
10         int heightR = heightOfBinaryTree(root.right);
11         if (heightL + heightR > maxDiff) maxDiff = heightL + heightR;
12         return Math.max(heightL, heightR) + 1;
13     }
14 }

更多讨论：

https://discuss.leetcode.com/category/696/diameter-of-binary-tree

543. Diameter of Binary Tree