Dominosa has one fixed six-tile board in this browser tool, not a selectable easy, medium, or hard level sequence. The board reads 0 0 1 on the first row and 1 2 2 on the second. Your task is to cover all six cells with three dominoes, place each domino on orthogonally adjacent uncovered cells, and use each unordered number pair no more than once. Because pair order is ignored, 1-2 and 2-1 count as the same pair. That makes this version a compact test of coverage, adjacency, and pair tracking rather than a game with several calibrated levels. The Dominosa tool provides arrow-key navigation, Space or Enter selection, exact scoring, restart, and an exhaustive deadlock detector. There is no timer, random board generator, or speed increase. A search for “dominosa difficulty levels” should therefore not be read as a promise that the interface contains multiple tiers: it contains one disclosed teaching board, while the same reasoning can be transferred to larger Dominosa positions.
Reading difficulty without level labels
For this product, difficulty is not an official tier assigned to a board. There is one disclosed layout, one fixed rule set, and no level selector, random generator, timer, or rising speed. The same controls and end conditions apply from the first selection onward. For searchers asking about “dominosa difficulty levels,” choosing “easy” or “hard” is not part of this tool’s operation.
Logical pressure can still change from move to move. A placement can have several viable neighbors, or it can consume a pair that later leaves an exposed cell without a legal partner. A position becomes more constrained when a cell has fewer uncovered orthogonal neighbors or the remaining values create repeated-pair conflicts. The supplied facts verify a clean column solution, but they do not establish that it is the only possible tiling. It is therefore accurate to call the column route a verified solution, not an official difficulty rating or a uniqueness claim.
Rules that define the challenge
Every placement must satisfy coverage, adjacency, and unordered-pair uniqueness at the same time. These fixed conditions create the puzzle’s difficulty:
| Rule or condition | Official behavior | Effect on the puzzle |
|---|---|---|
| Fixed board | The first row is 0 0 1, and the second row is 1 2 2. | Every new attempt starts from the same disclosed position. |
| Domino placement | A domino covers two uncovered cells that share an edge; diagonal contact does not count. | Values may look close, but their cell positions must still permit a legal connection. |
| Complete coverage | All six cells must belong to exactly one of three dominoes. | A partial arrangement is not a completed board. |
| Pair identity | Pairs are unordered, so 1-2 and 2-1 are identical. | A normalized pair ledger prevents accidental reuse from either direction. |
| Completion | Three accepted dominoes with three distinct value pairs must cover the board. | Covering every cell is necessary but not sufficient when a pair would be duplicated. |
| End conditions | A valid full cover completes the game; two invalid selections or a proven impossible remainder end the run. | Both careful planning and error control affect the result. |
Keep each candidate pair in a consistent order, such as writing every pair with the smaller value first. Once 0-1 has been used, a later 1-0 placement would repeat it. On the disclosed board, the vertical route creates 0-1, 0-2, and 1-2. Those pairs demonstrate the clean solution, but they are not a universal requirement for every Dominosa position.
Solve the disclosed six-tile board
The clearest way to learn the interface is to solve the supplied board in its three vertical columns. The following route uses the verified keyboard controls and produces three distinct pairs without leaving an uncovered cell.
- Read the board as two horizontal rows: 0 0 1 above 1 2 2. The goal is three dominoes, not one continuous six-cell line.
- Use the arrow keys to move the outlined cursor to the top-left 0. The cursor identifies which visible cell will receive the next selection.
- Press Space or Enter to anchor that top-left 0 as the first tile of a domino. Selecting the same anchored cell again before completion cancels the pending selection.
- Move straight down to the bottom-left 1 and press Space or Enter again. The cells are orthogonally adjacent and uncovered, so they form the accepted pair 0-1.
- Move the cursor to the top-middle 0 and select it. Move down to the bottom-middle 2, then press Space or Enter again to create 0-2.
- Move to the top-right 1 and select it. Move straight down to the bottom-right 2 and press Space or Enter to create 1-2.
- Check that all three columns are covered. The board is complete because all six cells belong to exactly one domino and the pairs 0-1, 0-2, and 1-2 are distinct.
- Do not attempt to reuse a covered cell. After a domino is accepted, its cells are disabled and cannot participate in another placement.
- Watch both failure limits during practice. A selection is invalid when its cells are not orthogonally adjacent or when their unordered pair has already been used; the second invalid selection creates a terminal failure state. Restart clears every domino, pending selection, mistake, and current point.
Each second selection converts the current anchor into a domino only after the placement passes the adjacency and unused-pair checks. Mouse and touch users can select the same visible cells, while the arrow-key route keeps the entire interaction focused and auditable.
Why the first pair can change everything
The two top-row 0 cells form a tempting opening because they touch horizontally and their 0-0 pair has not been used. That placement satisfies the immediate rules, yet it leaves no perfect completion. After covering those cells, the remaining legal connections are the right-column 1-2 pair, the bottom-left-to-bottom-middle 1-2 pair, and the bottom-middle-to-bottom-right 2-2 pair.
Taking either available 1-2 pair forces the remaining two cells to form the same 1-2 pair again. Taking 2-2 instead leaves two separated 1 cells with no uncovered edge between them. Neither route can cover the board legally. The opening therefore passes local validation but fails the more important test: whether a complete unique-pair tiling still exists.
After every accepted domino, Dominosa’s exhaustive detector examines the first uncovered tile, tries each uncovered orthogonal neighbor whose value pair remains unused, and recursively checks the remainder. If every possible branch fails, the run is marked deadlocked immediately. This check operates on the same game state used by the interface, so it detects a genuine logical dead end rather than relying on a simplified test board. This distinction between a locally legal move and a globally solvable position is the central difficulty in the six-tile puzzle.
Score, mistakes, and controls
Each accepted domino awards 400 points. A full valid finish therefore produces 3 accepted dominoes × 400 points = 1,200 points. There are no timing bonuses or speed multipliers; exact scoring comes entirely from completing valid dominoes.
| Control or board state | Exact result |
|---|---|
| Arrow keys | Move the outlined cursor between visible cells. |
| Space or Enter | Select the first tile, then select an orthogonally adjacent uncovered tile to form a domino. |
| Select the anchored cell again | Cancel the pending first selection. |
| Covered cell | Remains disabled and cannot be reused. |
| Restart | Clear all dominoes, selections, mistakes, and current points. |
| Double-press Escape | Replace the game with the spreadsheet-style Boss Key view; repeat the action to restore the unchanged board. |
| Mouse or touch | Select the same visible cells without changing the puzzle rules. |
An invalid selection is not the same as selecting a covered cell, which is disabled. Invalid selections are attempts to join nonadjacent cells or repeat an unordered pair, and two such attempts freeze the run in a terminal failure state. A proven dead end can end a run earlier even when no second mistake has occurred. Restart provides a clean reset, while the best score remains in local browser storage.
Carry the same reasoning to larger positions
Although this browser version remains fixed at six cells, larger Dominosa puzzles use the same central distinction: covering the board is insufficient if a placement would duplicate a value pair. Difficulty can increase through more constrained cells, more competing placements, or repeated values that narrow the available partners.
- Normalize every candidate pair so reversed values cannot hide an earlier use.
- Mark each accepted pair in a ledger before evaluating the next placement.
- Inspect edge cells and cells with fewer uncovered neighbors before committing.
- Ask whether every remaining cell can still belong to a valid completion, not merely whether the current pair looks reasonable.
On the disclosed teaching board, the vertical columns make the reasoning especially clear because their three pairs are distinct. That advice does not imply that this tool generates larger levels; it describes how the same coverage and uniqueness logic applies when more placements must be coordinated.
What counts as a demanding Dominosa position
A demanding position has fewer viable next placements, more risk of repeated pairs, or uncovered cells with limited neighbors. The most instructive complication occurs when a move passes every immediate check but removes the final possible completion. The horizontal 0-0 opening demonstrates that trap, while the three vertical dominoes demonstrate a clean finish. Because this Dominosa version contains one fixed board, those constraint interactions—not an easy-to-hard level list—are its useful difficulty lesson.