text: class TinyUrl:
      def __init__(self):
          self.seq_id = 0
          self.rec_shortToLong = {}
          self.rec_longToShort = {}
          self.chars = "0123456789abcedfghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
  
      """
      @param: url: a long url
      @return: a short url starts with http://tiny.url/
      """
      def longToShort(self, url):
          if url in self.rec_longToShort:
             return self.rec_longToShort[url]
  
          short_url = ""
          id = self.seq_id
          self.seq_id += 1
          while id > 0:
              short_url += self.chars[id % 62]
              id //= 62
  
          while len(short_url) < 6:
              short_url += self.chars[0]
  
          short_url = "http://tiny.url/" + short_url
  
          self.rec_shortToLong[short_url] = url
          self.rec_longToShort[url] = short_url
  
          return short_url
  
  
      """
      @param: url: a short url starts with http://tiny.url/
      @return: a long url
      """
      def shortToLong(self, url):
          if url in self.rec_shortToLong:
             return self.rec_shortToLong[url]
  
          return ""
  