Leetcode#17 Letter Combinations of a Phone Number

class Solution {
    public:
        vector<string> letterCombinations(string digits) {
            vector<string> lettComb;
            if (digits.size() == 0)
                return lettComb;
            lettComb.push_back("");
            string dict[] = {" ", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
            for(int i=0; i<digits.size(); i++) {
                int n = lettComb.size();
                string lett = dict[digits[i]-'0'];
                for(int j=0; j<n; j++) {
                    for(int k=1; k<lett.size(); k++) {
                        string comb = lettComb[j];  //clone lettComb[j]
                        comb.push_back(lett[k]);
                        lettComb.push_back(comb);
                    }
                    lettComb[j].push_back(lett[0]);
                }
            }
            return lettComb;
        }
};