How to Play
Welcome to Dominos. A small partition puzzle. Read on for the goal and a handful of solving strategies.
The goal
The board has N+1 columns by N rows of numbered cells (e.g. level 5 = 6×5 = 30 cells, divided into 15 dominoes). Click on grid lines between cells to mark a divider — that is, declare that the two cells are on opposite sides of a wall. Your goal: split the board into 2×1 dominoes such that EVERY possible value-pair from {0,0} up to {N,N} appears exactly once.
Solving strategies
- Move your mouse over a divider between two tiles — the player highlights every other pair on the board with the same combination. If you see only one possible pair, you are certain to pick it.
- After confirming a unique pair, look around for the side-effects: a same-value pair you previously had two candidates for may now have one impossible candidate, letting you commit the other.
- When there are multiple candidates for a pair, you can commit a "guess" route. Press the Bookmark button (⚑) first to save your state; if a contradiction appears several moves later, Recall (↺) brings you back to the bookmark and you can try the other route.
The control row
- Reset — clear all moves and start over (timer keeps running).
- Undo — revert the last move.
- Redo — re-apply a move you just undid.
- Bookmark (⚑) — save the current board state so you can come back to it.
- Recall (↺) — restore the most recently bookmarked state.
Interaction modes (mobile)
On mobile, the Tile / Bar / HL buttons switch how taps are interpreted. Desktop ignores them — clicking a divider directly always works.
- Tile mode — tap a cell to select it; tap two adjacent cells to mark a domino between them. Easiest for picking out a single pair quickly.
- Bar mode — tap the bar/divider between cells directly, same as desktop. Better when you want to mark multiple dividers quickly.
- HL (highlight) mode — tap any cell to highlight every other cell with the same value. Useful for spotting all candidates for a pair without committing anything.
When you solve it
The timer freezes and a green banner shows your time. You can play another puzzle at the same level (Replay) or pick a different one.