Encode and Decode TinyURL

这个题就是实现长网址变短网址的方法，实际上的做法和想象的用哈希函数是不一样的，我们不需要去基于长网址来生成短网址，而是可以按照九章课里面描述的纯随机生成六位码然后用哈希表（实际情况中就很像Cassandra这样的NoSQL数据库了）来存储对应关系即可，当然也可以用更复杂的Base62算法

class Codec:
    charList = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
    shortStore = {}

    def encode(self, longUrl):
        """Encodes a URL to a shortened URL.

        :type longUrl: str
        :rtype: str
        """
        shortUrl = ''
        for i in xrange(6):
            shortUrl += random.choice(self.charList)
        self.shortStore[shortUrl] = longUrl
        return shortUrl

    def decode(self, shortUrl):
        """Decodes a shortened URL to its original URL.

        :type shortUrl: str
        :rtype: str
        """
        return self.shortStore[shortUrl]

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