cool and pythonic solution to leetcode 17.

17. Letter Combinations of a Phone Number

Given a digit string, 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.

Input:Digit string "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

思路：hashtable+笛卡尔积

my code:

class Solution(object):
def letterCombinations(self, digits):
"""
:type digits: str
:rtype: List[str]
"""

if not digits:
return []

dict = {'2':['a','b','c'],
'3':['d','e','f'],
'4':['g','h','i'],
'5':['j','k','l'],
'6':['m','n','o'],
'7':['p','q','r','s'],
'8':['t','u','v'],
'9':['w','x','y','z'],
'1':['*'],
'0':[' ']
}
ll = [dict[key] for key in digits]

return [''.join(item) for item in itertools.product(*ll)]