/**
 * 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) {
        Queue<TreeNode> queue = new LinkedList<>();
        List<Integer> values = new LinkedList<>();
        if (root == null) {
            return values;
        }

        queue.offer(root);
        while (!queue.isEmpty()) {
            values.add(queue.peek().val);

            int size = queue.size();
            while (size > 0) {
                TreeNode curr = queue.poll();
                if (curr.right != null) {
                    queue.offer(curr.right);
                }
                if (curr.left != null) {
                    queue.offer(curr.left);
                }
                size--;
            }
        }

        return values;
    }
}