Leetcode 17. Letter Combinations of a Phone Number(水)

17. Letter Combinations of a Phone Number

Medium

Given a string containing digits from 2-9 inclusive, 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. Note that 1 does not map to any letters.

Example:

Input: "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.

class Solution {
public:
    vector<string> letterCombinations(string digits) {
        map<char,string> test;
        test['2'] = "abc";
        test['3'] = "def";
        test['4'] = "ghi";
        test['5'] = "jkl";
        test['6'] = "mno";
        test['7'] = "pqrs";
        test['8'] = "tuv";
        test['9'] = "wxyz";
        vector<string> fa_;
        vector<string> chil_;
        fa_.push_back("");
        for(int i = 0; i < digits.length(); i++){
            chil_.clear();
            for(int j = 0; j < fa_.size(); j++){
                //printf("%d %s",test[digits[i]].length());
                for(int k = 0; k < test[digits[i]].length(); k++){
                    //printf("%s",test[digits[i]][k]);
                    chil_.push_back(fa_[j]+test[digits[i]][k]);
                }
            }
            fa_ = chil_;
        }
        return chil_;
    }
};