Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

Example:

Input: "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
Note:

Although the above answer is in lexicographical order, your answer could be in any order you want.

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

我现在好像都在搬运柳婼的代码~~~~

就当是兔式刷题吧。

先刷到一定程度，再用java龟式刷题好好学习

class Solution {
public:
    vector<string> letterCombinations(string digits) {
        vector<string> result;
        if(digits.length()==0){
            return result;
        }
        result.push_back("");
        vector<string> v ={"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
        
        for(int i=0;i<digits.length();i++){
            string s= v[digits[i]-'0'];
            vector<string> temp;
            for(int j=0; j<s.length();j++){
                for(int k=0;k<result.size();k++){
                    temp.push_back(result[k]+s[j]);
                }
            }
            result=temp;
        }
        return result;
    }
};

柳婼题解，又短又快，又好理解~~·