public class Codec {
    private ArrayList<String> urls = new ArrayList<String>();
    // Encodes a URL to a shortened URL.
    public String encode(String longUrl) {
        urls.add(longUrl);
        return String.valueOf(urls.size() - 1);
    }

    // Decodes a shortened URL to its original URL.
    public String decode(String shortUrl) {
        int idx = Integer.valueOf(shortUrl);
        return idx > urls.size() ? "" : urls.get(idx);
    }
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.decode(codec.encode(url));