Renju is the professionalised Japanese form of the five-in-a-row family. Because moving first is a decisive advantage in plain gomoku, Renju forbids Black from playing certain overwhelming shapes, restoring balance to the game.
Variant implemented
Renju on 15×15 with the standard forbidden moves for Black (double-three, double-four, overline); White wins on five or more in a row. No opening exchange rule.
Board and pieces
15×15 intersections.
Setup
An empty board. Black plays first.
Turn
Place a stone on an empty intersection.
Capture and scoring
None.
Win condition
Black wins with exactly five in a row. White wins with five or more.
Draw condition
A full board with no five in a row is a draw.
Special rules
Because moving first is decisive in plain gomoku, Black is handicapped by three forbidden shapes: an overline (six or more in a row), a double-four, and a double-three. Making exactly five always wins and overrides the forbidden-move check. If Black is left with nothing but forbidden points, Black loses.
Computer opponent
Alpha-beta restricted to points near existing stones, with threat-based move ordering. Hard searches four plies and defends fours and open threes reliably.