剑指offer面试题63 二叉搜索树的第k个结点

class TreeNode {    int val = 0;    TreeNode left = null;    TreeNode right = null;    public TreeNode(int val) {        this.val = val;    }}public class Solution {private int index = 0;TreeNode KthNode(TreeNode pRoot, int k) {if (pRoot != null) {TreeNode node = KthNode(pRoot.left, k);if (node != null) {return node;}index++;if (index == k) {return pRoot;}node = KthNode(pRoot.right, k);if (node != null) {return node;}}return null;}}