Letter combinations of a Phone number--Leetcode

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

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

Input: Digit string "Output": ["Ad", "AE", "AF", "BD", "Be", "BF", "CD", "CE", "CF"].

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

Algorithm one: The combination of the thought of carrying the numeral.

Class Solution {public:vector<string> Lettercombinations (string digits) {const char *map[] = {"", "", "        ABC "," Def "," Ghi "," JKL "," MnO "," PQRS "," TUV "," WXYZ "};        int idx[sizeof (map)/sizeof (map[0]) = {0};        vector<string> result;        string item;        BOOL carry = false;                while (!carry) {item.clear ();                carry = true;                        for (int i=0; i<digits.size (); ++i) {const char * p = &map[digits[i]-' 0 '][idx[i]];                        if (*p) item.append (1, *p);                                if (carry && *p) {++idx[i];                                ++p;                                if (!*p) idx[i] = 0;                        else carry = false;      }} result.push_back (item);  } if (Result.empty ()) Result.push_back (item);    return result; }};

The following sentence is purely to satisfy the test case when the input of Leetcode is empty string (""):

        if (Result.empty ())                result.push_back (item);

See this algorithm execution time, can not help to do a, leave a memorial.

Algorithm two, to be continued

Letter combinations of a Phone number--Leetcode