python leetcode 17. Letter Combinations of a Phone Number

建立映射关系即可

class Solution(object):
    def letterCombinations(self, digits):
        """
        :type digits: str
        :rtype: List[str]
        """
        if digits=="":
            return []
        dict1={}
        dict1[2]="abc"
        dict1[3]="def"
        dict1[4]="ghi"
        dict1[5]="jkl"
        dict1[6]="mno"
        dict1[7]="pqrs"
        dict1[8]="tuv"
        dict1[9]="wxyz"
        res=[""]
        for d in digits:
            res1=[]
            for t in res:
                for s in dict1[int(d)]:
                    res1.append(t+s)
            res = res1 
        return res