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].

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

Solution: Compute the left height and right height of each node, update the max diameter every time.

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     private int maxDiameter = Integer.MIN_VALUE;
12     
13     public int diameterOfBinaryTree(TreeNode root) {
14         if (root == null || (root.left == null && root.right == null)) return 0;
15         
16         getHeight(root);
17         return maxDiameter;
18     }
19     
20     private int getHeight(TreeNode root) {
21         if (root == null) return 0;
22         if (root.left == null && root.right == null) return 1;
23         
24         int leftHeight = getHeight(root.left);
25         int rightHeight = getHeight(root.right);
26         maxDiameter = Math.max(maxDiameter, leftHeight + rightHeight);
27         return 1 + Math.max(leftHeight, rightHeight);
28     }
29 }