text: // Time:  O(26^2)
  // Space: O(1)
  
  // enumeration
  class Solution {
  public:
      vector<string> cellsInRange(string s) {
          vector<string> result;
          for (char x = s[0]; x <= s[3]; ++x) {
              for (char y = s[1]; y <= s[4]; ++y) {
                  result.push_back({x, y});
              }
          }
          return result;
      }
  };
  