EncodeAndDecodeTinyURL.java

//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.

public class EncodeAndDecodeTinyURL {
    HashMap<String, String> map = new HashMap<String, String>();
    String characters = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    int count = 1;

    public String getKey() {
        String key = "";
        while(count > 0) {
            count--;
            key += characters.charAt(count);
            count /= characters.length();
        }
        
        return key;
    }
    
    // Encodes a URL to a shortened URL.
    public String encode(String longUrl) {
        String key = getKey();
        map.put(key, longUrl);
        count++;
            
        return "http://tinyurl.com/" + key;
    }

    // Decodes a shortened URL to its original URL.
    public String decode(String shortUrl) {
        return map.get(shortUrl.replace("http://tinyurl.com/", ""));
    }
}

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