Binary Tree Right Side View

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.

Example:

Input: [1,2,3,null,5,null,4]
Output: [1, 3, 4]
Explanation:

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

class Solution {
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> ans = new ArrayList<>();
        if (root == null)
            return ans;
        Queue<TreeNode> q = new LinkedList<>();
        q.add(root);
        while (q.size() != 0) {
            int size = q.size();
            while (size-- > 0) {
                TreeNode node = q.poll();
                if (size == 0)
                    ans.add(node.val);
                if (node.left != null)
                    q.add(node.left);
                if (node.right != null)
                    q.add(node.right);
            }
        }
        return ans;
    }
}