Good question. Whenever the program goes to place a room or corridor, it firstly checks whether those squares are unoccupied. If not, the room/corridor isn't

Good question. Whenever the program goes to place a room or corridor, it firstly checks whether those squares are unoccupied. If not, the room/corridor isn't placed. I originally made it place the room anyway, since it might result in some interesting structures. But in practice, it just made a complete mess and there was no easy way to decide when to make the algorithm stop.