打卡群刷题总结0623——电话号码的字母组合

class Solution(object):
    def letterCombinations(self, digits):
        """
        :type digits: str
        :rtype: List[str]
        """
        if len(digits) == 0:
            return []

        digit = list(range(2, 10))
        alpha = ['abc', 'def', 'ghi', 'jkl', 'mno', 'pqrs', 'tuv', 'wxyz']
        d = {}
        for i, di in enumerate(digit):
            d[str(di)] = alpha[i]

        res = ['']
        for di in digits:
            tmp = []
            for alpha_i in d[di]:
                tmp.extend(list(map(lambda x: x + alpha_i, res)))
            res = tmp
        return res