Tic-tac-toe is a paper-and-pencil game for two players, X and O, who take turns marking the spaces in a 3×3 grid. The player who succeeds in placing three of their marks in a horizontal, vertical, or diagonal row wins the game. Players alternate placing Xs and Os on the grid until either (a) one player has three in a row horizontally, vertically, or diagonally; or (b) all of the spaces on the grid have been filled. If a player is able to draw three Xs or three Os in a row, that player wins. If all of the spaces on the grid are filled and there is no winner, the game is a draw.