text: #17. Letter Combinations of a Phone Number
  
  class Solution:
  	def letterCombinations(self, digits):
  		my_dict={'2':'abc','3':'def','4':'ghi','5':'jkl','6':'mno','7':'pqrs','8':'tuv','9':'wxyz'}
  
  		results=[]
  		for digit in digits:
  			if len(results)==0:
  				results=[iter for iter in my_dict[digit]]
  			else:
  				results=[first+new for first in results for new in my_dict[digit]]
  
  		return results
  
  
  """
  Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.
  
  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 1:
  
  Input: digits = "23"
  Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
  Example 2:
  
  Input: digits = ""
  Output: []
  Example 3:
  
  Input: digits = "2"
  Output: ["a","b","c"]
  """