LeetCode 515. Find Largest Value in Each Tree Row

 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> res = new ArrayList<>();
13         Queue<TreeNode> queue = new LinkedList<>();
14         
15         if(root != null) queue.offer(root);
16         
17         while(!queue.isEmpty()) {
18             int max = Integer.MIN_VALUE;
19             int size = queue.size();
20             for(int i = 0; i < size; i++) {
21                 TreeNode node = queue.poll();
22                 max = Math.max(max, node.val);
23                 if(node.right != null) queue.offer(node.right);
24                 if(node.left != null) queue.offer(node.left);
25             }
26             res.add(max);
27         }
28         
29         return res;
30     }
31 }