Binary Tree Right Side View leetcode

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

For example:
Given the following binary tree,

   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---

You should return [1, 3, 4].

public class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> res = new ArrayList<Integer>();
        if (root == null) {
            return res;
        }
        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode tem = queue.poll();
                if (i == size - 1) {
                    res.add(tem.val);
                }
                if (tem.left != null) {
                    queue.offer(tem.left);
                }
                if (tem.right != null) {
                    queue.offer(tem.right);
                }
            }
        }
        return res;
    }
}