/**

 * Definition for a binary tree node.

 * public class TreeNode {

 *     int val;

 *     TreeNode left;

 *     TreeNode right;

 *     TreeNode(int x) { val = x; }

 * }

 */

class Solution {

    public List<List<Integer>> levelOrder(TreeNode root) {

        List<List<Integer>> res=new ArrayList<List<Integer>>();

        if(root==null){

            return res;

        }

        LinkedList<TreeNode> que=new LinkedList<TreeNode>();

        que.offer(root);

        int curNode=1;

        ArrayList<Integer> list=new ArrayList<Integer>();

        while(!que.isEmpty()){

            root=que.poll();

            --curNode;

            if(root.left!=null){

                que.offer(root.left);

            }

            if(root.right!=null){

                que.offer(root.right);

            }

            list.add(root.val);

            if(curNode==0){

                curNode=que.size();

                res.add(list);

                list=new ArrayList<Integer>();

            }

        }

        return res;

    }

}