LeetCode – Refresh – Letter Combination of a Phone Number

 1 class Solution {
 2 private:
 3     unordered_map<char, string> dict;
 4 public:
 5     void getComb(vector<string> &result, string s, string current, int index) {
 6         if (current.size() == s.size()) {
 7             result.push_back(current);
 8             return;
 9         }
10         for (int i = 0; i < dict[s[index]].size(); i++) {
11             getComb(result, s, current + dict[s[index]][i], index+1);
12         }
13     }
14     vector<string> letterCombinations(string digits) {
15         vector<string> result;
16         if (digits.size() == 0) return result;
17         dict[‘2‘] = "abc";
18         dict[‘3‘] = "def";
19         dict[‘4‘] = "ghi";
20         dict[‘5‘] = "jkl";
21         dict[‘6‘] = "mno";
22         dict[‘7‘] = "pqrs";
23         dict[‘8‘] = "tuv";
24         dict[‘9‘] = "wxyz";
25         getComb(result, digits, "", 0);
26         return result;
27     }
28 };