富途笔试-找到搜索二叉树中两个错误的节点

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param root TreeNode类 the root
     * @return int整型一维数组
     */
    List<Integer> res = new ArrayList();
    public int[] findError (TreeNode root) {
        // write code here
        int[] r = new int[2];
        dfs(root);
        for(int i = 0; i < res.size(); i++){
            if(res.get(i) > res.get(i+1)){
               r[1] = res.get(i); 
                break;
            }
        }
        for(int j = res.size() - 1; j >= 0; j--){
            if(res.get(j) < res.get(j-1)){
                r[0] = res.get(j);
                break;
            }
        }
        return r;
    }
    
    public void dfs(TreeNode root){
        if(root != null){
            dfs(root.left);
            res.add(root.val);
            dfs(root.right);
        }
    }
}