SRM 344 Div2 Level 2

SRM 344 Div2 Level 2

class SimpleRotationDecoder
{

  vector<string> split(const string &str, const string &delim){
    vector<string> res;
    size_t current = 0, found, delimlen = delim.size();
    while((found = str.find(delim, current)) != string::npos){
      res.push_back(string(str, current, found - current));
      current = found + delimlen;
    }
    res.push_back(string(str, current, str.size() - current));
    return res;
  }

  vector<string> make_passwords(void){
    vector<string> passwords;
    for(size_t i = 0; i < 26; i++){
      for(size_t j = 0; j < 26; j++){
        for(size_t k = 0; k < 26; k++){
          char pass[4];
          pass[0] = i + 'a';
          pass[1] = j + 'a';
          pass[2] = k + 'a';
          pass[3] = '\0';
          passwords.push_back(pass);
        }
      }
    }
    return passwords;
  }

  int _c2i(char c){
    if(c == ' ')
      return 0;
    else
      return c - 'a' + 1;
  }

  char _i2c(int a){
    if(a == 0)
      return ' ';
    else
      return a - 1 + 'a';
  }

  //3 + 26 =  29 % 27 = 2
  //2 - 26 = -24 + 27 = 3

  string _decode(const string &cipher, const string &pass){
    string decode(cipher);
    for(size_t i = 0; i < cipher.size(); i++){
      int a = _c2i(cipher[i]) - _c2i(pass[i % 3]);
      if(a < 0) a += 27;
      decode[i] = _i2c(a);
    }
    return decode;
  }


  bool checkRule(string decoded){
    vector<string> words = split(decoded, " ");
    for(size_t i = 0; i < words.size(); i++) {
      string word = words[i];
      if(word.size() < 2 || word.size() > 8)
        return false;
      bool flg = false;
      for(size_t j = 0; j < word.size(); j++) {
        char c = word[j];
        if(c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u')
          flg = true;
      }
      if(!flg) return false;
    }
    return true;
  }


public:
  string decode(string cipherText)
  {
    vector<string> passwords = make_passwords();
    for(size_t i = 0; i < passwords.size(); i++){
      string decoded = _decode(cipherText, passwords[i]);
      if(checkRule(decoded)){
        return decoded;
      }
    }
    return string("");
  }
};