Refactor

src/s0017_letter_combinations_of_a_phone_number.cpp

@@ -1,6 +1,6 @@
 #include "s0017_letter_combinations_of_a_phone_number.hpp"
 
-vector<string> Solution::letterCombinations(string digits) {
+vector<string> S0017::letterCombinations(string digits) {
   unordered_map<string, vector<string>> map;
   map["2"] = vector<string>{"a", "b", "c"};
   map["3"] = vector<string>{"d", "e", "f"};