/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Codec {

    // Decodes your encoded data to tree.
    public TreeNode deserialize(String data) {
        String[] stringNodes = data.split(",");
        List<Integer> traversal = new ArrayList<Integer>();

        for (int i = 0; i < stringNodes.length; i++) {
            String node = stringNodes[i];

            if (node.equals("null")) {
                traversal.add(null);
            } else if (!node.isEmpty()) {
                traversal.add(Integer.parseInt(node));
            }
        }

        TreeNode root = null;

        if (traversal.size() > 0) {
            root = new TreeNode(traversal.get(0));

            int index = 1;

            Queue<TreeNode> queue = new ArrayDeque();
            queue.offer(root);

            while (!queue.isEmpty()) {
                for (int i = 0; i < queue.size(); i++) {

                    TreeNode node = queue.poll();

                    if (index < traversal.size()) {
                        Integer leftVal = traversal.get(index);

                        if (leftVal != null) {
                            node.left = new TreeNode(leftVal);
                            queue.offer(node.left);
                        }

                        index += 1;
                    }

                    if (index < traversal.size()) {
                        Integer rightVal = traversal.get(index);

                        if (rightVal != null) {
                            node.right = new TreeNode(rightVal);
                            queue.offer(node.right);
                        }

                        index += 1;
                    }
                }
            }
        }

        return root;
    }

    // Encodes a tree to a single string.
    public String serialize(TreeNode root) {

        // gettings traversal
        List<Integer> traversal = levelOrderTraversalWithNulls(root);

        // trim
        for (int i = traversal.size() - 1; i >= 0; i--) {
            if (traversal.get(i) != null) break;

            traversal.remove(i);
        }

        // building string
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < traversal.size(); i++) {
            sb.append(traversal.get(i));

            if (i != traversal.size() - 1) {
                sb.append(",");
            }
        }

        System.out.println(sb.toString());

        return sb.toString();
    }

    private List<Integer> levelOrderTraversalWithNulls(TreeNode root) {
        List<Integer> result = new ArrayList<Integer>();
        Queue<TreeNode> queue = new ArrayDeque<TreeNode>();

        if (root != null) {
            queue.offer(root);
            result.add(root.val);
        }

        while (!queue.isEmpty()) {
            for (int i = 0; i < queue.size(); i++) {
                TreeNode node = queue.poll();

                result.add(node.left == null ? null : node.left.val);
                result.add(node.right == null ? null : node.right.val);

                if (node.left != null) {
                    queue.offer(node.left);
                }

                if (node.right != null) {
                    queue.offer(node.right);
                }
            }
        }

        return result;
    }
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.deserialize(codec.serialize(root));