[leetcode]535. Encode and Decode TinyURL短网址的编解码器

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.

题意：
设计一个短网址的编解码器

code

 1 public class Codec {
 2  
 3     private static final String SEED = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
 4     private static final String BASE = "http://tinyurl.com/";
 5 
 6     private static Map<String, String> keyToURL = new HashMap<>();
 7     private static Map<String, String> urlToKey = new HashMap<>();
 8 
 9     public static void main(String[] args) {
10         String tinyURL = encode("http://thisislongurl.com/abcd/123");
11         String longURL = decode(tinyURL);
12 
13         System.out.println("tinyURL = " + tinyURL);
14         System.out.println("longURL = " + longURL);
15     }
16 
17     public static String encode(String longUrl) {
18         if (longUrl == null || longUrl.isEmpty()) {
19             return null;
20         }
21         if (urlToKey.containsKey(longUrl)) {
22             return BASE + urlToKey.get(longUrl);
23         }
24 
25         StringBuilder key = null;
26 
27         // keep generating keys until a unique one is found
28         do {
29             key = new StringBuilder();
30             for (int i = 0; i < 6; i++) {
31                 int r = (int)(Math.random() * SEED.length());
32                 key.append(SEED.charAt(r));
33             }
34         } while (keyToURL.containsKey(key));
35 
36         keyToURL.put(key.toString(), longUrl);
37         urlToKey.put(longUrl, key.toString());
38 
39         return BASE + key;
40     }
41 
42     public static String decode(String shortUrl) {
43         if (shortUrl == null || shortUrl.isEmpty()) {
44             return "";
45         }
46         String[] shortUrlSplits = shortUrl.split("/");
47         return keyToURL.get(shortUrlSplits[shortUrlSplits.length - 1]);
48     }
49 }