17 电话号码的字母组合

给定一个仅包含数字 2-9 的字符串，返回所有它能表示的字母组合。

给出数字到字母的映射如下（与电话按键相同）。注意 1 不对应任何字母。

示例:

输入："23"
输出：["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

解法

• Python

class Solution:
    def letterCombinations(self, string: str) -> List[str]:
        nine = [' ','','abc','def','ghi','jkl','mno','pqrs','tuv','wxyz']
        length = len(string)
        if length == 0: return []
        res = [None for i in range(length)]
        total = []
        def find(string,index):
            if length-index==1:
                for i in nine[eval(string)]:
                    res[length-1] = i
                    total.append(''.join(res.copy()))
                return

            for i in nine[eval(string[0])]:
                res[index]=i
                find(string[1:],index+1)
        find(string,0)
        return total