binary tree level order traversal

 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class  {
    public List<List<Integer>> levelOrder(TreeNode root) {
        LinkedList<TreeNode> search = new LinkedList<TreeNode>();
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        if(root==null) return res;
        search.add(root);
        while(!search.isEmpty()){
            int currentSize = search.size();
            List<Integer> subList = new ArrayList<Integer>();
            for(int i=0; i<currentSize;i++){
                TreeNode node = search.poll();
                subList.add(node.val);
                if(node.left!=null) search.offer(node.left);
                if(node.right!=null) search.offer(node.right);
            }
            res.add(subList);
        }
        return res;
    }
}