Imagine a grid of squares, like a tic-tac-toe board, that goes on infinitely in all directions.

Players alternate taking turns marking the board with X's and O's. The winner is the first player to get four marks in a row (horizontally, vertically, or diagonally).

On each turn, a player may either:

A: Place two of his/her marks on the board, or

B: Remove one of the other player's marks, and then place one of their own.

With optimal play, does either player have a forced win, or will this game continue on infinitely?

(In reply to Not so easy? by Caz)

Caz, in your scenario, X's 3rd move would be

X O
O X
    X
      X

for the win.

Posted by Ken Haley on 2006-06-10 18:50:28