LetterCombinationsPhone_DFS.cpp

class Solution {
private:
    vector<string> dic_s = {"", "", "abc", "def", "ghi","jkl", "mno","pqrs", "tuv", "wxyz"};
    vector<string> result;
public:
    void dfs(const string &digits, string s, int pos){
        int len = digits.size();
        if(pos >= len){
            return;
        }
        int subLen = dic_s[digits[pos] - '0'].size();
        for(int i = 0; i< subLen; i++)
        {
            string dic_string = dic_s[digits[pos] - '0'];
            string temp = s + dic_string[i];
            if(pos == len - 1)
            {
                result.push_back(temp);
            }
            dfs(digits, temp, pos + 1);
        }       
    }
    
    vector<string> letterCombinations(string digits) { 
        dfs(digits, "", 0);
        return result;
    }
};