class Solution {

public:

    vector<string> letterCasePermutation(string S) {

        vector<string> res;

        string add;

        DFS(res,S,,add);

        return res;

    }

    char func(char temp){

        if(temp >= &&temp <= ){

            temp -= ;

        }

        else if(temp <= &&temp >= ){

            temp += ;

        }

        return temp;

    }

    void DFS(vector<string>& res,string s,int pos,string add){

        if(add.size() == s.size()){

            res.push_back(add);

        }

        else{

            for(int i=pos;i < s.size();i++){

                char t = s[i];

                if(t >=  && t <= ){

                    add += s[i];

                }

                else{

                    string temp = add;

                    temp += func(t);

                    DFS(res,s,i+,temp);

                    add += s[i];

                }

            }

        if(add.size() == s.size()){ // 这里又加了个是因为害怕最后一个是数字

            res.push_back(add);

        }

        }

    }

};

class Solution {

public:

    vector<string> letterCasePermutation(string S) {

        vector<string> res;

        helper(S, , res);

        return res;

    }

    void helper(string& s, int pos, vector<string>& res) {

        if (pos == s.size()) {

            res.push_back(s);

            return;

        }

        helper(s, pos + , res);

        if (s[pos] > '') {

            s[pos] ^= ;

            helper(s, pos + , res);

        }

    }

};