LeetCode#543: Diameter of Binary Tree

Description

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

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

Solution

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
	private int res = 0;
	
    public int diameterOfBinaryTree(TreeNode root) {
        if(root == null) 
        	return res;
        depth(root);
        return res;
    }
    
    private int depth(TreeNode root) {
    	if(root == null) return 0;
    	int ld = depth(root.left);
    	int rd = depth(root.right);
    	res = Math.max(res, ld + rd);
    	return Math.max(ld, rd) + 1;
    }
}