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.

参考：http://www.cnblogs.com/TenosDoIt/p/3771254.html

与LeetCode:Subsets I II 类似

 

C++实现代码：

#include<iostream>

#include<vector>

#include<string>

using namespace std;



class Solution {

public:

    vector<string> letterCombinations(string digits) {

        vector<string> ret(1,"");

        if(digits.empty())

            return ret;

        string str[]={" ","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};

        size_t i,j,k;

        for(i=0;i<digits.size();i++)

        {

            string s=str[digits[i]-'0'];

            vector<string> tmp=ret;

            ret.clear();

            for(j=0;j<tmp.size();j++)

            {

                for(k=0;k<s.size();k++)

                    ret.push_back(tmp[j]+s[k]);

            }

        }

        return ret;

    }

};



int main()

{

    Solution s;

    vector<string> result=s.letterCombinations(string("31"));

    for(auto a:result)

        cout<<a<<endl;

}