LeetCode_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"].

　　水题： DFS

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    DFS( string & digit,int i, string s)

     {

        if(i == size){

            result.push_back(s);

            return ;

        }

        int index = digit[i] - '0' ;

    

        for(int j = 0; j < counts[index] ; j++)

        {                        

                        

            char c = letter[index]+j ;

                      

            DFS(digit, i+1, s+c);    

                                           

        }



    }

    vector<string> letterCombinations(string digits) {

        // Start typing your C/C++ solution below

        // DO NOT write int main() function

        result.clear();

        size = digits.size();



        

        string s = "";

        DFS(digits, 0 , s);

        

        return result ;

        

    }

private :

vector<string> result ;

int size ;

};