On the Subject of XO

Keep your strikes in line.

  • This module contains a 3x3 display, two arrow buttons on the right, a circular button between the two arrows, and a letter display on top. Pressing the arrows will cycle between six different games of tic-tac-toe.
  • Each board corresponds to a letter in an English word. The boards are ordered according to the word, but the module may not initialize at the beginning of the decrypted word. Pressing the circular button toggles between the boards and submission letters. In the submission phase, the 3×3 grid will display letters which, when pressed, are added to the top display; the arrows can be used to switch between three pages of letters. The bottom-right space on the third page can be used as a backspace button. Pressing the circular button again will exit the submission phase, but keep the currently inputted letters. Entering six letters will automatically submit the input and solve the module if correct, or strike and clear the input if incorrect.
Decrypting the Boards

Each board will have Xs and Os already in place, as well as a highlighted space. X places the first piece in each game; O and X alternate placing pieces afterwards. The board must be played out for it to be decrypted:

  • If it is a player’s turn and they can get three of their pieces in a row, column, or diagonal, they must do so.
  • Otherwise, if it is a player’s turn and they can block their opponent from completing a tic-tac-toe, they must do so. If there are multiple tic-tac-toes to be blocked, they must block using the first space in reading order.
  • Otherwise, gameplay freezes and the board state is final.

The highlighted space will now either be an X, an O, or empty.

To create the key used to translate the boards into letters, Caesar shift the fourth character of the serial number backwards by the sum of the serial number’s digits. Place the resulting letter in the slot marked by the exclamation point in the grid below. Move forward through the alphabet, placing letters into slots in reading order, wrapping around from the bottom-right to the top-left and leaving a blank slot in between Z and A.


___ ___ ___
___ _!_ ___
___ ___ ___


If the highlighted space is an X, use the left letter in the corresponding space in the grid above. Otherwise, if the space is empty, use the middle letter. Otherwise, if the space is an O, use the right letter.