leetcode-python-电话号码的字母组合

逐个遍历字典，逐个匹配

class Solution:
    def letterCombinations(self, digits: str) -> List[str]:
        if not digits:
            return []
        dic = {'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']}
        result = []
        for i in digits:
            temp = []
            for char in dic[i]:
                if not result:
                    temp.append(char)
                else:
                    for j in result:
                        temp.append(j+char)
            result = temp
        return result