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Tic-Tac-Toe Variants

In standard tic-tac-toe, the second player can force a draw, but the three-by-three grid is a somewhat artificial restriction, and in fact, given enough room, the first player could always achieve a three-in-a-row. This page is about tic-tac-toe-like games in which there is some pattern to achieve other than the three-in-a-row. Most of what appears here is from Martin Gardner's article, "Harary's Generalized Ticktacktoe", in The Colossal Book of Mathematics.

The idea of changing the goal of tic-tac-toe is almost as old as tic-tac-toe itself. In Japan, a five-in-a-row game called ninuki renju (which is, I believe, Japanese for the computer kicks my butt) is so popular that it has seen endless tinkering to reduce the inherent first-player advantage and bring the game into greater balance. The 20th-century combinatorist Frank Harary looked at games in which the goal was not necessarily n-in-a-row, but the achievement of some "animal". These animals are patterns of cells more commonly known as polyominoes; for example: (how these come out depends on how your browser displays tables. no promises.)

L-tromino "knobby" "tippy" Utah F-pentomino
Playing with any of these as the goal on a sufficiently large grid, Player 1 can always acheive on of the first three, while Player 2 can always prevent Player 1 from attaining either of the two pentominoes. Due to a strategy-stealing argument, these are the only two possible outcomes. Only three of the twelve pentominoes are attainable goals for Player 1. There are 35 species of hexominoes. All are known to have strategies by which the second player can force a draw, with one exception. Meet Snakey.

I haven't played with Snakey enough to have a sense of whether he is a first- or second-player win, although Ava, having never played at all, thinks she would rather play defense. (Since in theory Player 2 should never win outright, we will declare her the winner if Player 1 is unable to make a Snakey on a reasonable-sized grid, say 12-by-12.) It probably makes sense to play games in pairs, switching roles, to even things out.

Many more variations seem worth investigating -- give each player a different animal to try to make; play on different grids, etc.

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