1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public List<Integer> largestValues(TreeNode root) {
12         List<Integer> ans = new ArrayList<Integer>();
13         if (root == null) return ans;
14         Queue<TreeNode> queue = new LinkedList<TreeNode>();
15         queue.add(root);
16         while (queue.isEmpty() != true) {
17             int size = queue.size();
18             int max = Integer.MIN_VALUE;
19             for (int i = 0; i < size; i++) {
20                 TreeNode node = queue.poll();
21                 max = Math.max(max, node.val);
22                 if (node.left != null) queue.add(node.left);
23                 if (node.right != null) queue.add(node.right);
24             }
25             ans.add(max);
26         }
27         return ans;
28     }
29 }