题解 | #第k轻的牛牛#

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 root TreeNode类
     * @param k int整型
     * @return int整型
     */
    public void inorder(List<Integer>list, TreeNode root) {
        if (root == null) {
            return;
        }
        inorder(list, root.left);
        list.add(root.val);
        inorder(list, root.right);
    }
    public int kthLighest (TreeNode root, int k) {
        List<Integer>list = new ArrayList<>();
        inorder(list, root);
       
       return list.get(k-1);
    }
}