题解 | #二叉搜索树的第k个节点#

二叉搜索树的中序遍历为有序序列，可以先中序遍历，再获得第K个位置的值

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 {
    public int KthNode (TreeNode proot, int k) {
        // write code here
        if(proot == null || k==0){
            return -1;
        }
        ArrayList res = new ArrayList();
        inOrder(proot,res);
        if(k>res.size()){
            return -1;
        }
        return res.get(k-1);
    }
    public void inOrder(TreeNode root,ArrayList res){
        if(root == null){
            return;
        }
        inOrder(root.left,res);
        res.add(root.val);
        inOrder(root.right,res);
    }
}