# Solution to N-tris

### by Oliver Kosut

Given are two simultaneous, partially interacting, Tetris-like games. These games differ from ordinary Tetris in the following ways:

• the number of squares in the polyominoes vary widely
• polyominoes cannot be rotated
• each polyomino is either black or white
• the full queue of upcoming pieces is shown
• when a line is completed, it does not disappear
• there is no gravity
• each game allows 17 or 18 rejections; when a piece is rejected it moves to the end of the opposite game's queue.

If a piece spills over the top of the playing field, you get "Game Over". You'll note that the total number of squares in both queues is exactly the number of squares in the entire playing field. Therefore, the only way to avoid losing is to completely fill the playing field. There is only one way to do this, during which you will need to use every allowed rejections for both games. Solving the games produces a 21x21 grid of black and white squares, which turns out to be a QR code. Use your Blackberry (or another smart phone, or an online decoder) to decode it, and it resolves to the answer QUEUER (which sounds a little like "QR").

The following image shows how to solve the games. Polyominoes are labeled by the order in which they are placed in their respective game.

Behind-the-scenes note: You may have wondered where the knitting puzzle was in this hunt. Well, this is it! The original concept for this puzzle was that a knitting pattern would be given that would produce the QR code for QUEUER. Cally Perry, James Whiting, and Mira Whiting put a lot of work into writing that version of the puzzle, but for various reasons it didn't work out. We still liked the QUEUER/QR pun, so we came up with this idea to replace it.