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 int kthLighest (TreeNode root, int k) {
        // write code here
        List<Integer> result = new ArrayList();
        inorder(root,result);
        return result.get(k-1);
    }

    public void inorder(TreeNode root,List<Integer> list){
        if(root == null){
            return;
        }

        inorder(root.left,list);
        list.add(root.val);
        inorder(root.right,list);
    }
}