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.
1 class Solution { 2 unordered_map<char, vector<string>> ht = { 3 {‘0‘, {" "}}, {‘1‘, {""}}, {‘2‘, {"a", "b", "c"}}, {‘3‘, {"d", "e", "f"}}, 4 {‘4‘, {"g", "h", "i"}}, {‘5‘, {"j", "k", "l"}}, {‘6‘, {"m", "n", "o"}}, 5 {‘7‘, {"p", "q", "r", "s"}}, {‘8‘, {"t", "u", "v"}}, {‘9‘, {"w", "x", "y", "z"}}, 6 }; 7 public: 8 vector<string> letterCombinations(string digits) { 9 vector<string> ret; 10 int n = digits.size(); 11 12 if (n == 0) return ret; 13 14 if (n == 1) return ht[digits[0]]; 15 16 vector<string> prev = letterCombinations(digits.substr(0, n - 1)); 17 18 for (auto s : prev){ 19 for (int i = 0; i < ht[digits[n-1]].size(); i++) 20 ret.push_back(s+ht[digits[n-1]][i]); 21 } 22 23 return ret; 24 } 25 };
[LeetCode] 17. Letter Combinations of a Phone Number
原文：http://www.cnblogs.com/amadis/p/5926503.html