/**

  * Definition for a binary tree node.

  * public class TreeNode {

  *     int val;

  *     TreeNode left;

  *     TreeNode right;

  *     TreeNode(int x) { val = x; }

  * }

  */

 public class Solution {

     public List<Integer> largestValues(TreeNode root) {

         List<Integer> ans = new ArrayList<Integer>();

         if (root == null) return ans;

         Queue<TreeNode> queue = new LinkedList<TreeNode>();

         queue.add(root);

         while (queue.isEmpty() != true) {

             int size = queue.size();

             int max = Integer.MIN_VALUE;

             for (int i = 0; i < size; i++) {

                 TreeNode node = queue.poll();

                 max = Math.max(max, node.val);

                 if (node.left != null) queue.add(node.left);

                 if (node.right != null) queue.add(node.right);

             }

             ans.add(max);

         }

         return ans;

     }

 }