535. Encode and Decode TinyURL

▶ 要求给出一种对 URL 网址进行压缩和解压的算法，例如 https://leetcode.com/problems/design-tinyurl ←→ http://tinyurl.com/4e9iAk，在不允许打表的情况下应该无法压缩的。

● 代码，6 ms，完全不压缩，just for fun

 class Solution
 {
 public:
     // Encodes a URL to a shortened URL.
     string encode(string longUrl) { return longUrl; }
     // Decodes a shortened URL to its original URL.
     string decode(string shortUrl) { return shortUrl; }
 };

 class Solution
 {
 public:
     string theLatestUrl;
     string encode(string longUrl) { theLatestUrl = longUrl; return "whatever, doesn't matter"; }
     string decode(string shortUrl) { return theLatestUrl; }
 };

● 代码，9 ms，随机数打表法，加密之后的字符串只与原网址字符串在表中的存放位置有关，与其内容无关。类似的有各种打表法，需要依赖散列表来解码，时间复杂度 O(1)，空间开销大。

 class Solution
 {
 public:
     unordered_map<string, string> um;
     string encode(string longUrl)
     {
         const string baseUrl = "http://tinyurl.com/";
         int r;
         string ran;
         srand();
         for (r = rand() % , ran = to_string(r); um.count(baseUrl + ran) == ; r = rand() % , ran = to_string(r));
             // 随机取一个空的位置把网址放进去
         um[baseUrl + ran] = longUrl;
         return baseUrl + ran;
     }
     string decode(string shortUrl)
     {
         if (um.count(shortUrl) == )
             return um[shortUrl];
         return "";
     }
 };