text: #include "pangram.h"
  
  #include <cctype>
  
  namespace pangram {
  
  bool is_pangram(const std::string &str) {
      bool table[26] = {};
      for (char c : str) {
          if (!isalpha(static_cast<int>(c))) {
              continue;
          }
  
          int lower = std::tolower(static_cast<int>(c));
          int index = lower - 'a';
  
          table[index] = true;
      }
  
      for (bool b : table) {
          if (!b) {
              return false;
          }
      }
  
      return true;
  }
  
  } // namespace pangram
  