回复：能否详细说明一下，或者给出伪代码?学习学习

Let's see a simple example. There are only 4 rooms, initilized to 0000 (not cleaned), you print the value after 1 min, you get a number, say 3, 0011, the 1's are the bits (rooms) changed. This test question is simpler than page management in OS because the bit which have been changed to 1 will never changed back to 0 in 24 hours.
Certainly, you have to write a small function to display the 'human readable' output - .