题解 | #牛群的最长距离#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
     int max = 0;
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param root TreeNode类
     * @return int整型
     */
    public int diameterOfBinaryTree (TreeNode root) {
        // write code here
        diameter(root);
        return max;
    }
     
    private int diameter(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int left = diameter(root.left);
        int right = diameter(root.right);
        max = Math.max(max, left + right);
        return Math.max(left, right) + 1;
    }
}