LeetCode 017 Letter Combinations of a Phone Number

题目描述：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"].

分析：

递归

 

代码如下：

class Solution {

private:

    map<char, vector<char> > dict;

    vector<string> ret;

public:

    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 dep, int maxDep, string &s, string ans){

        if (dep == maxDep){

            ret.push_back(ans);

            return;

        }

        

        for(int i = 0; i < dict[s[dep]].size(); i++)

            dfs(dep + 1, maxDep, s, ans + dict[s[dep]][i]);

    }

    

    vector<string> letterCombinations(string digits) {

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

        // DO NOT write int main() function

        ret.clear();

        createDict();

        dfs(0, digits.size(), digits, "");

        return ret;

    }

};