New ctci quetsion: 18.3: find largest word box in list of million words
Attempt 1 at word square challenge, failed
word square challenge code finds word squares but is iniefficient.
Trying to optimize word square puzzle but it isn't going tooooooo well.
Adding 2 more CTCI problems from 'hard' set of questions: largest word rectangle and finding subgrid where corners are black (I misread the problem, should be all BORDERS are black :-()