sad

map<int, string> numberMap;
    vector<string> dfs(string digits , int index){
        if(index == digits.size()){
            return {""};
        }
        vector<string> ans = dfs(digits , index+1);
        string possibleChar = numberMap[digits[index] - '0'];
        vector<string> letters;
        for(auto ch : possibleChar){

            for(auto str : ans){
                letters.push_back(ch + str);
            }
        }
        return letters;

    }
    vector<string> letterCombinations(string digits) {
        if(digits.size()==0){
            return {};
        }
        numberMap[2] = "abc";
        numberMap[3] = "def";
        numberMap[4] = "ghi";
        numberMap[5] = "jkl";
        numberMap[6] = "mno";
        numberMap[7] = "pqrs";
        numberMap[8] = "tuv";
        numberMap[9] = "wxyz";
        return dfs(digits ,0);

    }