Crosswise dominoes Puzzles

Rules — Crosswise dominoes

• The board starts empty. Players take turns placing one domino, which covers exactly two adjacent squares.
• Player 1 places only vertical dominoes (blue) and player 2 only horizontal ones (maroon). You never get to choose the other orientation.
• Dominoes may not overlap or stick out of the board.
• Whoever cannot place a domino on their turn loses. There are no draws and nothing is counted: the game simply ends when someone runs out of room.

Levels:

• Level 1 — 4×4 board.
• Level 2 — 6×6 board.
• Level 3 — 8×8 board.

The two sides are not interchangeable: vertical and horizontal are different games to play. That is exactly the point — play both sides before deciding which one you prefer.

Blue plays vertically. On this empty 4×3 board blue had 8 possible placements and maroon had 9. Blue places a single domino in the second column — and look at what dies: the four horizontal placements marked ✕ are now impossible, because they all needed one of the two squares just taken.

The count after that one move: blue 8 → 6, maroon 9 → 5. The domino cost blue two of its own moves and cost maroon four of theirs.

That is the whole game. You are not trying to fill the board, you are trying to run out of room later than your opponent. A domino placed across the middle takes a lot from them; one squeezed against the edge usually takes very little.