题解 | #二叉搜索树的第k个节点#

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
     */
    public int KthNode (TreeNode proot, int k) {
        // write code here -> list来存放中序遍历遍历的值
        ArrayList<Integer> list = new ArrayList<>();
        inOrder(list, proot);
        if(list.size() < k || proot == null || k == 0)return -1;

        return list.get(k - 1);
    }

    public void inOrder(List list, TreeNode proot){
        if(proot == null)return;
        inOrder(list, proot.left);
        list.add(proot.val);
        inOrder(list, proot.right);
    }
}