leetcode之-题17

class Solution(object):
    def combine(self, str1, str2):
        """
        :type str1: list[str]
        :type str2: list[str]
        :rtype: list[str]
        """
        """
        对两个list进行合并，比如['a','b']和['d','e'合并为['ad','ae','bd','be']
        """
        ret = []
        if len(str1) == 0:
            return str2
        if len(str2) == 0:
            return str1
        for x in str1:
            for y in str2:
                ret.append(x+y)
        return ret

    def letterCombinations(self, digits):
        """
        :type digits: str
        :rtype: List[str]
        """
        ret = []
        if len(digits) == 0:
            return ret
        dic = dict({'2':'abc','3':'def','4':'ghi','5':'jkl','6':'mno','7':'pqrs','8':'tuv','9':'wxyz'})
        for x in digits:
            str2 = list(dic[x])
            ret = self.combine(ret,str2)
        return ret