Leetcode 535 Encode and Decode 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.

编码的方式可以有很多种，因为一般都会受到Integer范围的限制，所以说可以选择固定长度的编码形式

public class Codec {    String alphabet =  "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";    Random r = new Random();    Map<String, String> map = new HashMap<>();    String key = getString();    private String getString(){        StringBuffer sb = new StringBuffer();        for(int i = 0; i < 6; i++){            sb.append(alphabet.charAt(r.nextInt(62)));        }        return sb.toString();    }    // Encodes a URL to a shortened URL.    public String encode(String longUrl) {        while(map.containsKey(key)){            key = getString();        }        map.put(key, longUrl);        return "http://tinyurl.com/" + key;    }    // Decodes a shortened URL to its original URL.    public String decode(String shortUrl) {        return map.get(shortUrl.replace("http://tinyurl.com/", ""));    }}// Your Codec object will be instantiated and called as such:// Codec codec = new Codec();// codec.decode(codec.encode(url));