题目链接：二叉搜索树的第k个结点

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 {/*** 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 proot TreeNode类 * @param k int整型 * @return int整型*/TreeNode res = new TreeNode(-1);int count = 0;public int KthNode (TreeNode root, int k) {// 二叉搜索树：中序遍历为递增序列的二叉树if(root == null || k <= 0) return -1;this.count = k;dfs(root);return res.val;}public void dfs(TreeNode root){if(root == null) return;dfs(root.left);count --;if(count == 0){res = root;return;}if(count > 0) dfs(root.right);}}