Tic-tac-toe – the suicide move

Tic-tac-toe is the one minute game – probably the most played by children – where two players put noughts and crosses on a 3 x 3 grid with the goal to be the first one having three in one row.

Recently somebody started a game while putting his nought in the center of the grid. After the second player (me) put his cross in an edge the first player said that this was a bad move. Instead I should have played side-middle. As an experienced tic-tac-toe player I knew that he was wrong but he tried to argue that he was.

Ok, then let’s see how right he was. Here player one plays the noughts while the second one plays the crosses.

As mentioned his first move was the grid center. According to his suggestion the second player should put his cross right below it. Player one’s next move could then be the right upper edge.

As of now he has two in a diagonal row. Thus he forces the second player to put his cross in the opposite edge. Player one is choosing the right bottom edge. Interesting! There are now two crosses to be made by player two to not loose the game.

So if the first player starts with the center the second player must choose an edge. In this case the strategy for the second player is to avoid the guaranteed suicide and draw level at least.

For the readers being mathematician, according the German Wikipedia there are 255168 runs of play of which 131184 lead to a winning situation for the first player and 77904 for the second player. 46080 are draws. These numbers only consider the cases with three noughts or crosses in a row or diagonal and a full occupied grid. The pre-game over situations are remained out of consideration.

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