【LeetCode with Python】 Letter Combinations of a Phone Number

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原题页面： https://oj.leetcode.com/problems/letter-combinations-of-a-phone-number/
题目类型：
难度评价：★
本文地址： http://blog.youkuaiyun.com/nerv3x3/article/details/37335129

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"].

Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.

class Solution:
    # @return a list of strings, [s1, s2]
    def letterCombinations(self, digits):
        map = {
               "0":  (),
               "1":  (),
               "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")
               }
        result1 = [ "" ]
        result2 = [ ]
        for ch in digits:
            list = map[ch]
            if 0 == len(list):
                continue
            for str in result1:
                for suffix in list:
                    result2.append(str + suffix)
            result1 = result2
            result2 = [ ]
        return result1