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  • Leetcode: Encode and Decode TinyURL

    Note: This is a companion problem to the System Design problem: Design 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.
    
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    1. 根据系统设计的Estimation of the amount of data we need to store for the next couple of years, 我们应需要6位Base62的char来encode

    2. assume 避免地址爆炸,相同的longUrl得到相同的shortUrl, 这需要一个额外的hashMap longToShort

    3. 这里因为我们想保证都是6位的shortURL,所以采用random generate的方法;其他方法还可以是编号等等

     1 public class Codec {
     2     HashMap<String, String> hashToUrl = new HashMap<String, String>();
     3     HashMap<String, String> urlToHash = new HashMap<String, String>();
     4     String tinyUrlBase = "http://tinyurl.com/";
     5     String characters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
     6     Random random = new Random();
     7 
     8     // Encodes a URL to a shortened URL.
     9     public String encode(String longUrl) {
    10         if (urlToHash.containsKey(longUrl))
    11             return tinyUrlBase + urlToHash.get(longUrl);
    12             
    13         StringBuilder hash = new StringBuilder();
    14         do {
    15             for (int i=0; i<6; i++) {
    16                 hash.append(characters.charAt(random.nextInt(characters.length())));
    17             }
    18         } while (hashToUrl.containsKey(hash.toString()));
    19         
    20         hashToUrl.put(hash.toString(), longUrl);
    21         urlToHash.put(longUrl, hash.toString());
    22         return tinyUrlBase + hash.toString();
    23     }
    24 
    25     // Decodes a shortened URL to its original URL.
    26     public String decode(String shortUrl) {
    27         return hashToUrl.get(shortUrl.substring(tinyUrlBase.length()));
    28     }
    29 }
    30 
    31 // Your Codec object will be instantiated and called as such:
    32 // Codec codec = new Codec();
    33 // codec.decode(codec.encode(url));
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  • 原文地址:https://www.cnblogs.com/EdwardLiu/p/6533835.html
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