Letter Combinations of a Phone Number

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.

Example:

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

 

Code:

class Solution {public:    map<char,vector<char>> dict;    vector<string> ret;    void CreateDict()    {        dict.clear();        dict['2'].push_back('a');        dict['2'].push_back('b');        dict['2'].push_back('c');        dict['3'].push_back('d');        dict['3'].push_back('e');        dict['3'].push_back('f');        dict['4'].push_back('g');        dict['4'].push_back('h');        dict['4'].push_back('i');        dict['5'].push_back('j');        dict['5'].push_back('k');        dict['5'].push_back('l');        dict['6'].push_back('m');        dict['6'].push_back('n');        dict['6'].push_back('o');        dict['7'].push_back('p');        dict['7'].push_back('q');        dict['7'].push_back('r');        dict['7'].push_back('s');        dict['8'].push_back('t');        dict['8'].push_back('u');        dict['8'].push_back('v');        dict['9'].push_back('w');        dict['9'].push_back('x');        dict['9'].push_back('y');        dict['9'].push_back('z');    }        void DFS(int curDep,int len,string &s,string ans)    {        if(curDep==len)        {            ret.push_back(ans);            return ;        }        for(int i=0;i<dict[s[curDep]].size();i++)            DFS(curDep+1,len,s,ans+dict[s[curDep]][i]);    }        vector<string> letterCombinations(string digits) {        ret.clear();        CreateDict();        DFS(0,digits.size(),digits,"");        return ret;    }};