515. Find Largest Value in Each Tree Row

You need to find the largest value in each row of a binary tree.

Example:

Input: 

          1
         / \
        3   2
       / \   \  
      5   3   9 

Output: [1, 3, 9]

/**
 * 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> result = new ArrayList<Integer>();
        if(root == null){
            return result;
        }
        Queue<TreeNode> q = new LinkedList<TreeNode>();
        q.offer(root);
        while(!q.isEmpty()){
            int size = q.size();
            int max = Integer.MIN_VALUE;
            for(int i=0; i<size; i++){
                TreeNode cur = q.poll();
                max = Math.max(cur.val, max);
                if(cur.left != null){
                    q.offer(cur.left);
                }
                if(cur.right != null){
                    q.offer(cur.right);
                }
            }
            result.add(max);
        }
        return result;
    }
}