Letter Combinations of a Phone Number

Given a digit string, return all possible letter combinations that the number could 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 could be in any order you want.

思路：

深搜

代码：

    string table[10] = {"","", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
    void search(vector<string> &result, string tmp, string digits, int cur){
        if(cur == digits.length()){
            result.push_back(tmp);
            return;
        }
        tmp += " ";
        for(int i = 0; i < table[digits[cur]-'0'].length(); i++){
            tmp[cur] = table[digits[cur]-'0'][i];
            search(result, tmp, digits, cur+1);
        }
    }
    vector<string> letterCombinations(string digits) {
        vector<string> result;
        string tmp = "";
        search(result, tmp, digits, 0);
        return result;
    }