Canadian Checkers

Object of the game

Capture all of your opponent’s pieces or block them. The board has 144 squares; you play on the 72 dark squares, numbered 1 to 72. Each side lines up 30 men in five rows and White moves first.

A little history

Canadian checkers appeared in Quebec in the eighteenth century. They take the rules of international draughts onto a larger board: games are longer and more strategic, and multi-jumps can become spectacular.

Movement and captures

• The man moves one square diagonally and captures forwards as well as backwards.
• The king is flying: it travels along a whole free diagonal and, when capturing, lands on any free square beyond the captured piece.
• Capture is mandatory and the sequence that takes the most pieces must be played (majority capture, a king counting as one man).
• Captured pieces are removed only at the end of the sequence and cannot be jumped twice (Turkish strike).
• A man becomes a king if it ends its move on the last row; if it merely passes through it during a multi-jump, it stays a man.

End of the game

• You win if your opponent has no pieces left or can no longer move.
• Draw by threefold repetition, after 25 moves by each side played only with kings without a capture, or when a lone king holds out for 16 moves against three pieces including a king (5 moves against two pieces or fewer).

Controls

• Tap a piece then its destination square, or drag it.
• When a capture is mandatory, the pieces concerned are circled in red and only legal capture sequences are offered.
• If several capture sequences lead to the same square, then tap one of the pieces circled in purple to specify your choice.
• Playable squares carry the official numbering. The move list uses official notation: 32-28 for a move, 19x28 for a capture.
• Esc cancels the selection. The Undo and Hint buttons are in the top bar.

About the AI

A dedicated engine, written for Ludo Genie, runs in the background: complete generation of capture sequences (majority capture, Turkish strike), negamax alpha-beta search with a principal-variation window and iterative deepening, a transposition table with Zobrist keys, extension of captures and threats (quiescence), cautious reductions of late moves, killer moves and history for move ordering.

The evaluation weighs material (a king is worth about three men), the advancement and tempo of the men, control of the centre, the solidity of formations, the defence of the back row, mastery of the main diagonal and the handling of endgames. At Master level, the AI thinks for about three seconds per move and often sees more than ten plies ahead, much further in forced captures. The lower levels limit the depth and sometimes pick a weaker move, the way a human player would.