LeetCode - 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 

          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; }
 * }
 */
public class Solution {
    int d = 0;
    public int diameterOfBinaryTree(TreeNode root) {
        if (root == null)
            return 0;
        depth(root);
        return d;
    }
    
    private int depth(TreeNode node) {
        if (node == null)
            return 0;
        int left = depth(node.left);
        int right = depth(node.right);
        if (left + right > d)
            d = left + right;
        return left>right?left+1:right+1;
    }
    
}