给定一个二叉树的 根节点 root，想象自己站在它的右侧，按照从顶部到底部的顺序，返回从右侧所能看到的节点值。

示例 1:

输入: [1,2,3,null,5,null,4]
输出: [1,3,4]
示例 2:

输入: [1,null,3]
输出: [1,3]
示例 3:

输入: []
输出: []

提示:

二叉树的节点个数的范围是 [0,100]
-100 <= Node.val <= 100

注意：本题与主站 199 题相同：https://leetcode-cn.com/problems/binary-tree-right-side-view/

本题就是把最左边的节点改成最右边

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> list = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        if (root == null) {
            return list;
        }
        queue.offer(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode t = queue.poll();
                if (i == 0) {
                    list.add(t.val);
                }  
                if (t.right != null) {
                    queue.offer(t.right);
                }
                if (t.left != null) {
                    queue.offer(t.left);
                }
            }
        }
        return list;
    }
}