题解 | #二叉树的直径#

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 {

    private int res = 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
        getDepth(root);
        return res;
    }

    private int getDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int left = getDepth(root.left);
        int right = getDepth(root.right);
        res = Math.max(res, left + right);
        return Math.max(left, right) + 1;
    }
}