Tofu – The opposite of a font
<i>WARNING: PLEASE DO NOT RUN THIS CODE ON A HARD DRIVE, I'M NOT SURE HOW LONG IT WOULD TAKE. I USED A RAM DISK</i><p>I haven't looked at the implementation, but this seems to imply it is very I/O intensive and already takes a very long time in RAM. Yet, nothing about the problem statement suggests it would be such a task --- it sounds like something that could be very straightforwardly done completely in memory.