535. Encode and Decode TinyURL

Note: This is a companion problem to the System Design problem: Design
TinyURL.

TinyURL is a URL shortening service where you enter a URL such as ​​https://leetcode.com/problems/design-tinyurl​​​ and it returns a short URL such as ​​http://tinyurl.com/4e9iAk​​.

Design the encode and decode methods for the TinyURL service. There is no restriction on how your encode/decode algorithm should work. You just need to ensure that a URL can be encoded to a tiny URL and the tiny URL can be decoded to the original URL.

public class Codec {
    List<String> url = new ArrayList<>();
    // Encodes a URL to a shortened URL.
    public String encode(String longUrl) {
        url.add(longUrl);
        return "http://tinyurl.com/" + (url.size()-1);
    }

    // Decodes a shortened URL to its original URL.
    public String decode(String shortUrl) {
        String[] ss = shortUrl.split("/");
        int n = Integer.parseInt(ss[ss.length-1]);
        return url.get(n);
    }
}

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