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public class Codec {
    // Serialize the tree to a string
    public String serialize(TreeNode root) {
        if (root == null) {
            return "";
        }
        StringBuilder sb = new StringBuilder();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);

        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            if (node == null) {
                sb.append("null,");
            } else {
                sb.append(node.val).append(",");
                queue.add(node.left);
                queue.add(node.right);
            }
        }
        // Remove the trailing comma
        sb.setLength(sb.length() - 1);
        return sb.toString();
    }

    // Deserialize the string back to a tree
    public TreeNode deserialize(String data) {
        if (data == null || data.isEmpty()) {
            return null;
        }
        String[] nodes = data.split(",");
        TreeNode root = new TreeNode(Integer.parseInt(nodes[0]));
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);

        int i = 1;
        while (!queue.isEmpty() && i < nodes.length) {
            TreeNode current = queue.poll();

            // Process the left child
            if (!nodes[i].equals("null")) {
                current.left = new TreeNode(Integer.parseInt(nodes[i]));
                queue.add(current.left);
            }
            i++;

            // Process the right child
            if (i < nodes.length && !nodes[i].equals("null")) {
                current.right = new TreeNode(Integer.parseInt(nodes[i]));
                queue.add(current.right);
            }
            i++;
        }

        return root;
    }
}