Program: 164374
Project: 164374
Buggy source:
@Override protected boolean build(){
  if (!initRooms()) {
    return false;
  }
  int distance;
  int retry=0;
  int minDistance=(int)Math.sqrt(rooms.size());
  do {
    do {
      roomEntrance=Random.element(rooms);
    }
 while (roomEntrance.width() < 4 || roomEntrance.height() < 4);
    do {
      roomExit=Random.element(rooms);
    }
 while (roomExit == roomEntrance || roomExit.width() < 4 || roomExit.height() < 4);
    Graph.buildDistanceMap(rooms,roomExit);
    distance=roomEntrance.distance();
    if (retry++ > 10) {
      return false;
    }
  }
 while (distance < minDistance);
  roomEntrance.type=Type.ENTRANCE;
  roomExit.type=Type.EXIT;
  HashSet<Room> connected=new HashSet<Room>();
  connected.add(roomEntrance);
  Graph.buildDistanceMap(rooms,roomExit);
  List<Room> path=Graph.buildPath(rooms,roomEntrance,roomExit);
  Room room=roomEntrance;
  for (  Room next : path) {
    room.connect(next);
    room=next;
    connected.add(room);
  }
  Graph.setPrice(path,roomEntrance.distance);
  Graph.buildDistanceMap(rooms,roomExit);
  path=Graph.buildPath(rooms,roomEntrance,roomExit);
  room=roomEntrance;
  for (  Room next : path) {
    room.connect(next);
    room=next;
    connected.add(room);
  }
  int nConnected=(int)(rooms.size() * Random.Float(0.5f,0.7f));
  while (connected.size() < nConnected) {
    Room cr=Random.element(connected);
    Room or=Random.element(cr.neigbours);
    if (!connected.contains(or)) {
      cr.connect(or);
      connected.add(or);
    }
  }
  if (Dungeon.shopOnLevel()) {
    Room shop=null;
    for (    Room r : roomEntrance.connected.keySet()) {
      if (r.connected.size() == 1 && r.width() >= 5 && r.height() >= 5) {
        shop=r;
        break;
      }
    }
    if (shop == null) {
      return false;
    }
 else {
      shop.type=Room.Type.SHOP;
    }
  }
  specials=new ArrayList<Room.Type>(Room.SPECIALS);
  if (Dungeon.bossLevel(Dungeon.depth + 1)) {
    specials.remove(Room.Type.WEAK_FLOOR);
  }
  if (Dungeon.isChallenged(Challenges.NO_ARMOR)) {
    specials.remove(Room.Type.CRYPT);
  }
  if (Dungeon.isChallenged(Challenges.NO_HERBALISM)) {
    specials.remove(Room.Type.GARDEN);
  }
  assignRoomType();
  paint();
  paintWater();
  paintGrass();
  placeTraps();
  return true;
}

Fixed version (ground truth):
@Override protected boolean build(){
  if (!initRooms()) {
    return false;
  }
  int distance;
  int retry=0;
  int minDistance=(int)Math.sqrt(rooms.size());
  do {
    do {
      roomEntrance=Random.element(rooms);
    }
 while (roomEntrance.width() < 4 || roomEntrance.height() < 4);
    do {
      roomExit=Random.element(rooms);
    }
 while (roomExit == roomEntrance || roomExit.width() < 4 || roomExit.height() < 4);
    Graph.buildDistanceMap(rooms,roomExit);
    distance=roomEntrance.distance();
    if (retry++ > 10) {
      return false;
    }
  }
 while (distance < minDistance);
  roomEntrance.type=Type.ENTRANCE;
  roomExit.type=Type.EXIT;
  HashSet<Room> connected=new HashSet<Room>();
  connected.add(roomEntrance);
  Graph.buildDistanceMap(rooms,roomExit);
  List<Room> path=Graph.buildPath(rooms,roomEntrance,roomExit);
  Room room=roomEntrance;
  for (  Room next : path) {
    room.connect(next);
    room=next;
    connected.add(room);
  }
  Graph.setPrice(path,roomEntrance.distance);
  Graph.buildDistanceMap(rooms,roomExit);
  path=Graph.buildPath(rooms,roomEntrance,roomExit);
  room=roomEntrance;
  for (  Room next : path) {
    room.connect(next);
    room=next;
    connected.add(room);
  }
  int nConnected=(int)(rooms.size() * Random.Float(0.5f,0.7f));
  while (connected.size() < nConnected) {
    Room cr=Random.element(connected);
    Room or=Random.element(cr.neigbours);
    if (!connected.contains(or)) {
      cr.connect(or);
      connected.add(or);
    }
  }
  if (Dungeon.shopOnLevel()) {
    Room shop=null;
    for (    Room r : roomEntrance.connected.keySet()) {
      if (r.connected.size() == 1 && r.width() >= 5 && r.height() >= 5) {
        shop=r;
        break;
      }
    }
    if (shop == null) {
      return false;
    }
 else {
      shop.type=Room.Type.SHOP;
    }
  }
  specials=new ArrayList<Room.Type>(Room.SPECIALS);
  if (Dungeon.bossLevel(Dungeon.depth + 1)) {
    specials.remove(Room.Type.WEAK_FLOOR);
  }
  if (Dungeon.isChallenged(Challenges.NO_ARMOR)) {
    specials.remove(Room.Type.CRYPT);
  }
  if (Dungeon.isChallenged(Challenges.NO_HERBALISM)) {
    specials.remove(Room.Type.GARDEN);
  }
  if (!assignRoomType())   return false;
  paint();
  paintWater();
  paintGrass();
  placeTraps();
  return true;
}