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 

          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.

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

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private int maxDiameter = Integer.MIN_VALUE;
    
    public int diameterOfBinaryTree(TreeNode root) {
        if (root == null || (root.left == null && root.right == null)) return 0;
        
        getHeight(root);
        return maxDiameter;
    }
    
    private int getHeight(TreeNode root) {
        if (root == null) return 0;
        if (root.left == null && root.right == null) return 1;
        
        int leftHeight = getHeight(root.left);
        int rightHeight = getHeight(root.right);
        maxDiameter = Math.max(maxDiameter, leftHeight + rightHeight);
        return 1 + Math.max(leftHeight, rightHeight);
    }
}