encode-and-decode-tinyurl.py

# Time:  O(1)
# Space: O(n)

# 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.

class Codec:
    def __init__(self):
        self.__random_length = 6
        self.__tiny_url = "http://tinyurl.com/"
        self.__alphabet = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
        self.__lookup = {}


    def encode(self, longUrl):
        """Encodes a URL to a shortened URL.
        
        :type longUrl: str
        :rtype: str
        """
        def getRand():
            rand = []
            for _ in xrange(self.__random_length):
                rand += self.__alphabet[random.randint(0, len(self.__alphabet)-1)]
            return "".join(rand)
        
        key = getRand()
        while key in self.__lookup:
            key = getRand()
        self.__lookup[key] = longUrl
        return self.__tiny_url + key
        

    def decode(self, shortUrl):
        """Decodes a shortened URL to its original URL.
        
        :type shortUrl: str
        :rtype: str
        """
        return self.__lookup[shortUrl[len(self.__tiny_url):]]
        

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