//////////////////////////////////////
// Class for nodes of the binary tree.
class QuestionNode {
public:
  string text;
  QuestionNode *yes, *no;
  
  QuestionNode(string t, QuestionNode *y= NULL, QuestionNode *n= NULL) {
    text= t;
	yes= y;
	no= n;
  }
  
/////////////////////////////////////////
// Write out serialised form of the tree.
static void Save(ofstream &out, QuestionNode *qN, unsigned depth) {
  for (unsigned i= 0; i < depth; i++) out << "  ";
  
  if (qN == NULL) { out << "N:" << endl;
  } else { 
    out << "T: " << qN->text << endl;
	Save(out, qN->yes, depth+1);
	Save(out, qN->no, depth+1);
  }
}
    
///////////////////////////////////////
// Read in serialised form of the tree.
static QuestionNode *Load(ifstream &in) {
  string line;
  getline(in,line);
  unsigned nB= 0;
  while (nB < line.length() && line[nB] == ' ') nB++; // Skip leading blanks.
  
  if (line.substr(nB,2) == "N:") {
    return NULL;
  } else if (line.substr(nB,3) == "T: ") {
    return new QuestionNode(line.substr(nB+3), Load(in), Load(in));
  } else {
    cout << "Load error." << endl;
	exit(1);
  }
  return NULL; // To supress compile-time warning; it can "never" get here.
}

  QuestionNode *& nextQuestion();
  bool guessed();
};