短链系统设计(design tiny url)

- sql 需要自己写代码来 scale
- nosql，这些都帮你做了

public String long2Short(String url) {
  while(true) {
    String shortURL = randomShortURL();
    if (!databse.filter(shortURL=shortURL).exists()) {
      database.create(shortURL=shortURL, longURL=url);
      return shortURL;
    }
  }
  
}

public class TinyUrl {
    
    public TinyUrl() {
        long2Short = new HashMap<String, String>();
        short2Long = new HashMap<String, String>();
    }

    /**
     * @param url a long url
     * @return a short url starts with http://tiny.url/
     */
    public String longToShort(String url) {
        if (long2Short.containsKey(url)) {
            return long2Short.get(url);
        }

        while (true) {
            String shortURL = generateShortURL();
            if (!short2Long.containsKey(shortURL)) {
                short2Long.put(shortURL, url);
                long2Short.put(url, shortURL);
                return shortURL;
            }
        }
    }

    /**
     * @param url a short url starts with http://tiny.url/
     * @return a long url
     */
    public String shortToLong(String url) {
        if (!short2Long.containsKey(url)) {
            return null;
        }

        return short2Long.get(url);
    }

    private String generateShortURL() {
        String allowedChars = "0123456789" + "abcdefghijklmnopqrstuvwxyz" + "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

        Random rand = new Random();
        String shortURL = "http://tiny.url/";
        for (int i = 0; i < 6; i++) {
            int index = rand.nextInt(62);
            shortURL += allowedChars.charAt(index);
        }

        return shortURL;
    }
}

public class TinyUrl {
    public static int GLOBAL_ID = 0;
    private HashMap<Integer, String> id2url = new HashMap<Integer, String>();
    private HashMap<String, Integer> url2id = new HashMap<String, Integer>();

    private String getShortKey(String url) {
        return url.substring("http://tiny.url/".length());
    }

    private int toBase62(char c) {
        if (c >= '0' && c <= '9') {
            return c - '0';
        }
        if (c >= 'a' && c <= 'z') {
            return c - 'a' + 10;
        }
        return c - 'A' + 36;
    }

    private int shortKeytoID(String short_key) {
        int id = 0;
        for (int i = 0; i < short_key.length(); ++i) {
            id = id * 62 + toBase62(short_key.charAt(i));
        }
        return id;
    }

    private String idToShortKey(int id) {
        String chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
        String short_url = "";
        while (id > 0) {
            short_url = chars.charAt(id % 62) + short_url;
            id = id / 62;
        }
        while (short_url.length() < 6) {
            short_url = "0" + short_url;
        }
        return short_url;
    }

    /**
     * @param url a long url
     * @return a short url starts with http://tiny.url/
     */
    public String longToShort(String url) {
        if (url2id.containsKey(url)) {
            return "http://tiny.url/" + idToShortKey(url2id.get(url));
        }
        GLOBAL_ID++;
        url2id.put(url, GLOBAL_ID);
        id2url.put(GLOBAL_ID, url);
        return "http://tiny.url/" + idToShortKey(GLOBAL_ID);
    }

    /**
     * @param url a short url starts with http://tiny.url/
     * @return a long url
     */
    public String shortToLong(String url) {
        String short_key = getShortKey(url);
        int id = shortKeytoID(short_key);
        return id2url.get(id);
    }
}

public class TinyUrl2 {
    private HashMap<String,String> s2l = new HashMap<String,String>();
    private HashMap<String,String> l2s = new HashMap<String,String>();
    private int cnt = 0;
    private final StringBuffer tinyUrl = new StringBuffer("http://tiny.url/");
    private final String charset = "qwertyuiopasdfghjklzxcvbnm1234567890QWERTYUIOPASDFGHJKLZXCVBNM";
    
    private String newShortUrl() {
        StringBuffer res = new StringBuffer();
        for (int i = 0, j = cnt; i < 6; i++, j /= 62)
            res.append(charset.charAt(j % 62));
        cnt++;
        return tinyUrl + res.toString();
    }
    
    /*
     * @param long_url: a long url
     * @param key: a short key
     * @return: a short url starts with http://tiny.url/
     */
    public String createCustom(String long_url, String key) {
        String short_url = tinyUrl + key;
        if (l2s.containsKey(long_url)) {
            if (l2s.get(long_url).equals(short_url))
                return short_url;
            else
                return "error";
        }
        if (s2l.containsKey(short_url))
            return "error";
        l2s.put(long_url, short_url); 
        s2l.put(short_url, long_url);
        return short_url;
    }

    /*
     * @param long_url: a long url
     * @return: a short url starts with http://tiny.url/
     */
    public String longToShort(String long_url) {
        if (l2s.containsKey(long_url))
            return l2s.get(long_url);
        String short_url = newShortUrl(); 
        l2s.put(long_url, short_url); 
        s2l.put(short_url, long_url);
        return short_url; 
    }

    /*
     * @param short_url: a short url starts with http://tiny.url/
     * @return: a long url
     */
    public String shortToLong(String short_url) {
        if (s2l.containsKey(short_url))
            return s2l.get(short_url);
        return "error";
    }
}