No Four in a Row

Rules

Place either an ’X’ or an ’O’ into each empty cell such that four consecutive ’X’s or ’O’s do not appear horizontally, vertically or diagonally.

(Rules and example from WPC 2014 IB)

Rule variations

• In theory, substituting four-in-a-row constraint with any-number-in-a-row constraint works. Most commonly, the number is either 3 or 4.
• Binaire, Binoxxo, Tic-Tac-Logic, Takuzu, etc are all names given to a variant of No Three in a Row with an additional constraint that (i) in each row/column, number of X's and O's are the same and (ii) no two rows/columns are identical. This variant has been independently invented multiple times circa late 2000s, for example Binaire was patented by Frank Coussement and Peter De Schepper (Belgium) in 2009.

History of the puzzle

Tic-Tac-Toe (American) or Noughts and Crosses (British) is a game that has been played at least since the Roman times.

Appearances in the past WPCs

• WPC 2017/Round 12 by Ashish Kumar
• WPC 2017/Round 13 (Binaire) by Deb Mohanty
• WPC 2015/Round 3 by Andrey Bogdanov
• WPC 2014/Round 3