Find Largest Value in Each Tree Row

Input:

1
/ \
3   2
/ \   \
5   3   9

Output: [1, 3, 9]

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> result = new ArrayList<Integer>();
13         helper(root, result, 0);
14         return result;
15     }
16
17     private void helper(TreeNode root, List<Integer> result,int level) {
18         if (root == null) return;
19
20         if (result.size() < level + 1) {
21             result.add(new Integer(Integer.MIN_VALUE));
22         }
23         result.set(level, Math.max(result.get(level), root.val));
24
25         helper(root.left, result, level + 1);
26         helper(root.right, result, level + 1);
27     }
28 }