International Draughts

Object of the game

Capture all of your opponent’s pieces, or block them. The board has 100 squares; you play on the 50 dark squares, numbered 1 to 50. Each side starts with 20 men and White moves first.

Movement

• The man moves one square diagonally. It captures forwards and backwards, by jumping over an adjacent enemy piece to the free square just behind it.
• The king is flying: it moves along the whole length of a free diagonal and, when capturing, may land on any free square beyond the captured piece.

Captures

• Capture is mandatory. A multi-jump chains several captures in the same move.
• Majority capture: you must choose the sequence that takes the greatest number of pieces, a king counting as one man. If tied, the choice is free.
• Captured pieces stay on the board until the end of the sequence and cannot be jumped twice: this is the Turkish strike, which can block a king.

Promotion

• A man that ends its move on the last row becomes a king. If it merely passes through it during a multi-jump and moves on, 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.