#include "s0017_letter_combinations_of_a_phone_number.hpp"

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"};
  map["4"] = vector<string>{"g", "h", "i"};
  map["5"] = vector<string>{"j", "k", "l"};
  map["6"] = vector<string>{"m", "n", "o"};
  map["7"] = vector<string>{"p", "q", "r", "s"};
  map["8"] = vector<string>{"t", "u", "v"};
  map["9"] = vector<string>{"w", "x", "y", "z"};
  if (digits.length() == 0) {
    return vector<string>{};
  } else {
    string last = digits.substr(digits.length() - 1, 1);
    digits.pop_back();
    vector<string> combinations = letterCombinations(digits);
    if (combinations.size() == 0) {
      combinations = {""};
    }
    vector<string> result = {};
    for (int i{0}; i < map.at(last).size(); i++) {
      vector<string> temp = combinations;
      for (int j{0}; j < temp.size(); j++) {
        temp[j] += map.at(last)[i];
      }
      result.insert(result.end(), temp.begin(), temp.end());
    }
    return result;
  }
}