The top two answers are each interesting in their own way. The second answer, about the alternating colors, shows an elegant proof by induction.<p>The first (And accepted) answer, shows how important it is to account for edge cases! It also shows why legal contracts can be very long.
The first answer (5 Ts and 5 Ls) is quite interesting. Has anyone tried it with only using Ts and not using any other piece? Can we clear the game with even number of Ts?
I recently learned that the rules of Tetris are surprisingly subtle. For example, depending on how piece rotation is implemented, it may or may not be possible to clear three lines with a T piece ("T-spin triple").
I don't understand this answer: <a href="http://math.stackexchange.com/a/80814" rel="nofollow">http://math.stackexchange.com/a/80814</a>