LeetCode Letter Combinations of a Phone Number

题目：

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.

class Solution {public:vector<string> letterCombinations(string digits) {ans.clear();createDic();dfs(0, digits.size(), digits);return ans;}private://建立映射关系unordered_map<char, vector<char>> dic;vector<string> ans;char a[1000];void createDic() {dic['2'].push_back('a');dic['2'].push_back('b'); dic['2'].push_back('c');dic['3'].push_back('d');dic['3'].push_back('e');dic['3'].push_back('f');dic['4'].push_back('g');dic['4'].push_back('h');dic['4'].push_back('i');dic['5'].push_back('j');dic['5'].push_back('k');dic['5'].push_back('l');dic['6'].push_back('m');dic['6'].push_back('n');dic['6'].push_back('o');dic['7'].push_back('p');dic['7'].push_back('q');dic['7'].push_back('r');dic['7'].push_back('s');dic['8'].push_back('t');dic['8'].push_back('u');dic['8'].push_back('v');dic['9'].push_back('w');dic['9'].push_back('x');dic['9'].push_back('y');dic['9'].push_back('z');}void dfs(int dep, int maxDep, string &digits) {if (dep == maxDep) {string s;for (int i = 0; i < maxDep; i++)s.push_back(a[i]);ans.push_back(s);}for (int i = 0; i < dic[digits[dep]].size(); i++) {a[dep] = dic[digits[dep]][i];dfs(dep + 1, maxDep, digits);}}};