new_contents: """Leetcode 17. Letter Combinations of a Phone Number
  Medium
  
  URL: https://leetcode.com/problems/letter-combinations-of-a-phone-number/
  
  Given a string containing digits from 2-9 inclusive, return all possible 
  letter combinations that the number could represent.
  
  A mapping of digit to letters (just like on the telephone buttons) is 
  given below. Note that 1 does not map to any letters.
  
  Example:
  Input: "23"
  Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
  
  Note:
  Although the above answer is in lexicographical order, 
  your answer could be in any order you want.
  """
  
  class Solution(object):
      def letterCombinations(self, digits):
          """
          :type digits: str
          :rtype: List[str]
          """
          pass
  
  
  def main():
      pass
  
  
  if __name__ == '__main__':
      main()
  
subject: Add lc017_letter_combinations_of_a_phone_number.py