535. Encode and Decode TinyURL

Question

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.

Solution

• Method 1: HashMap + hashCode

  public class Codec {
      private Map<Integer, String> map = new HashMap<>();
      private int index;
      // Encodes a URL to a shortened URL.
      public String encode(String longUrl) {
          int key = longUrl.hashCode();
          this.map.put(key, longUrl);
          return "http://tinyurl.com/" + longUrl.hashCode();
      }
  
      // Decodes a shortened URL to its original URL.
      public String decode(String shortUrl) {
          return map.get(Integer.parseInt(shortUrl.replace("http://tinyurl.com/", "")));
      }
  }
  
  // Your Codec object will be instantiated and called as such:
  // Codec codec = new Codec();
  // codec.decode(codec.encode(url));
  

• Method 2: HashMap + count

  public class Codec {
      private Map<Integer, String> map = new HashMap<>();
      private int index;
      // Encodes a URL to a shortened URL.
      public String encode(String longUrl) {
          this.map.put(index, longUrl);
          return "http://tinyurl.com/" + index++;
      }
  
      // Decodes a shortened URL to its original URL.
      public String decode(String shortUrl) {
          return map.get(Integer.parseInt(shortUrl.replace("http://tinyurl.com/", "")));
      }
  }
  
  // Your Codec object will be instantiated and called as such:
  // Codec codec = new Codec();
  // codec.decode(codec.encode(url));
  

Amazon session

public class Codec {
    private static final String prefix = "http://tinyurl.com/";
    private Map<String, String> map = new HashMap<>();
    // Encodes a URL to a shortened URL.
    public String encode(String longUrl) {
        String hash = "" + longUrl.hashCode();
        map.put(hash, longUrl);
        return prefix + hash;
    }

    // Decodes a shortened URL to its original URL.
    public String decode(String shortUrl) {
        int index = shortUrl.lastIndexOf("/");
        String hash = shortUrl.substring(index + 1);
        return map.get(hash);
    }
}

// Your Codec object will be instantiated and called as such:
// Codec codec = new Codec();
// codec.decode(codec.encode(url));