[daily question] 535 Encryption and decryption of tinyurl

535. TinyURL Encryption and decryption
Reference resources ：https://leetcode.cn/problems/encode-and-decode-tinyurl/solution/tinyurl-de-jia-mi-yu-jie-mi-by-leetcode-ty5yp/
subject ：
Encoding and decoding
TinyURL It's a kind of URL Simplify services , such as ： When you enter a URL https://leetcode.com/problems/design-tinyurl when , It will return a simplified URL http://tinyurl.com/4e9iAk .
Please design a class to encrypt and decrypt TinyURL .
Realization Solution class ：

• Solution() initialization TinyURL System object .
• String encode(String longUrl) return longUrl Corresponding TinyURL .
• String decode(String shortUrl) return shortUrl The original URL . The subject data guarantees a given shortUrl Is encrypted by the same system object .

Answer key ：
About the short URL Common “ encryption ” Method or idea

• Self increasing id
  

String str = “ How do you do , I'm six six !”;
int i = str.lastIndexOf(“,”);

The output is zero 3.

lastIndexOf The result of is the subscript of the character . Subscript from 0 Start .

String str2 = str.substring(str.lastIndexOf(“,”));

The output is zero ：, I'm six six !

substring Start with this character .

public class Codec {
    
    private Map<Integer, String> dataBase = new HashMap<Integer, String>();
    private int id;

    public String encode(String longUrl) {
    
        id++;
        dataBase.put(id, longUrl);
        return "http://tinyurl.com/" + id;
    }

    public String decode(String shortUrl) {
    
        int p = shortUrl.lastIndexOf('/') + 1;
        int key = Integer.parseInt(shortUrl.substring(p));
        return dataBase.get(key);
    }
}

• Hash generation
  

public class Codec {
    
    static final int K1 = 1117;
    static final int K2 = 1000000007;
    private Map<Integer, String> dataBase = new HashMap<Integer, String>();
    private Map<String, Integer> urlToKey = new HashMap<String, Integer>();

    public String encode(String longUrl) {
    
        if (urlToKey.containsKey(longUrl)) {
    
            return "http://tinyurl.com/" + urlToKey.get(longUrl);
        }
        int key = 0;
        long base = 1;
        for (int i = 0; i < longUrl.length(); i++) {
    
            char c = longUrl.charAt(i);
            key = (int) ((key + (long) c * base) % K2);
            base = (base * K1) % K2;
        }
        while (dataBase.containsKey(key)) {
    
            key = (key + 1) % K2;
        }
        dataBase.put(key, longUrl);
        urlToKey.put(longUrl, key);
        return "http://tinyurl.com/" + key;
    }

    public String decode(String shortUrl) {
    
        int p = shortUrl.lastIndexOf('/') + 1;
        int key = Integer.parseInt(shortUrl.substring(p));
        return dataBase.get(key);
    }
}

Random generation

public class Codec {
    
    private Map<Integer, String> dataBase = new HashMap<Integer, String>();
    private Random random = new Random();

    public String encode(String longUrl) {
    
        int key;
        while (true) {
    
            key = random.nextInt();
            if (!dataBase.containsKey(key)) {
    
                break;
            }
        }
        dataBase.put(key, longUrl);
        return "http://tinyurl.com/" + key;
    }

    public String decode(String shortUrl) {
    
        int p = shortUrl.lastIndexOf('/') + 1;
        int key = Integer.parseInt(shortUrl.substring(p));
        return dataBase.get(key);
    }
}