public class Solution {

public ArrayList<ArrayList<Integer>> levelOrder\(TreeNode root\) {

    ArrayList result = new ArrayList\(\);



    if \(root == null\)

        return result;



    Queue<TreeNode> queue = new LinkedList<TreeNode>\(\);

    queue.offer\(root\);



    while \(!queue.isEmpty\(\)\) {

        ArrayList<Integer> level = new ArrayList<Integer>\(\);

        int size = queue.size\(\);

        for \(int i = 0; i < size; i++\) {

            TreeNode head = queue.poll\(\);

            level.add\(head.val\);

            if \(head.left != null\)

                queue.offer\(head.left\);

            if \(head.right != null\)

                queue.offer\(head.right\);

        }

        result.add\(level\);

    }



    return result;

}

}