【LeetCode】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"].

题意：输入一个数字字符串，返回每个数字键之间，所对应字母的所有组合

思路：每遍历到一个数字，把这个数字中的所有字符和原列表中的所有字符串相加

class Solution(object):
    def letterCombinations(self, digits):
        """
        :type digits: str
        :rtype: List[str]
        """
        if digits=='':
            return []
        flag={'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'],
        '0':[' ']
            }
        t = flag[digits[0]]
        res = t
        for c in digits[1:]:
            t = flag[c]
            res = [i+j for i in res for j in t]
        return res