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.

解法来自：https://leetcode.com/problems/encode-and-decode-tinyurl/discuss/100270/Three-different-approaches-in-java 

Approach 1- Using simple counter

 1 public class Codec {
 2     Map<Integer, String> map = new HashMap<>();
 3     int i=0;
 4     public String encode(String longUrl) {
 5         map.put(i,longUrl);
 6         return "http://tinyurl.com/"+i++;
 7     }
 8     public String decode(String shortUrl) {
 9         return map.get(Integer.parseInt(shortUrl.replace("http://tinyurl.com/", "")));
10     }
11 }

Approach 2- using hashcode

 1 public class Codec {
 2     Map<Integer, String> map = new HashMap<>();
 3     public String encode(String longUrl) {
 4         map.put(longUrl.hashCode(),longUrl);
 5         return "http://tinyurl.com/"+longUrl.hashCode();
 6     }
 7     public String decode(String shortUrl) {
 8         return map.get(Integer.parseInt(shortUrl.replace("http://tinyurl.com/", "")));
 9     }

Approach 3- using random function

 1 public class Codec {
 2     Map<Integer, String> map = new HashMap<>();
 3     Random r=new Random();
 4     int key=r.nextInt(10000);
 5     public String encode(String longUrl) {
 6         while(map.containsKey(key)) {
 7             key= r.nextInt(10000);
           }
 8         map.put(key,longUrl);
 9         return "http://tinyurl.com/"+key;
10     }
11     public String decode(String shortUrl) {
12         return map.get(Integer.parseInt(shortUrl.replace("http://tinyurl.com/", "")));
13     }
14 }