[Leetcode] letter combinations of a phone number

Question:

Given a digit string, return all possible letter combinations that the number coshould represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

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

Note:
Although the above answer is in lexicographical order, your answer cocould be in any order you want.

An1_1:

int counts[] = {0, 0, 3, 3, 3, 3, 3, 4, 3, 4};char letter[] = {'0', '0', 'a', 'd', 'g', 'j', 'm', 'p', 't', 'w'};        class Solution {public:    void comb(vector<string> &result, string &str, string &digits, int pos, int size) {        if (pos == size)        {            result.push_back(str);      // save results            return;        }                int j = digits[pos]-'0';        for (int i = 0; i < counts[j]; ++i)        {            str[pos] = letter[j] + i;            comb(result, str, digits, pos+1, size);        }    }        vector<string> letterCombinations(string digits) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        int nSize = digits.size();        string str(nSize, ' ');        vector<string> result;                comb(result, str, digits, 0, nSize);        return result;    }};

An1_2:

class Solution {public:    vector<string> letterCombinations(string digits) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        vector<string> result;                getRet(digits, "", 0, result);        return result;    }        void getRet(string digits, string s, int pos, vector<string>  &result) {        const static string dic[10]={ "0","1","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};        int size = digits.size();                if(pos == size) {            result.push_back(s);    // save result        }                int num = digits[pos] - '0';        for( int i=0; i<dic[num].size(); i++)   // assemble letters        {            string tmp = s;            tmp += dic[num][i];            getRet(digits, tmp, pos+1, result);        }    }};

Reference recommendations:

Letter combinations of a phone number