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Lizely

Mosaic Puzzle

Classify every square as black or white until each clue matches its clipped 3×3 neighborhood count.

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How to use

  1. 1.Move with the arrow keys; press Space for black or Enter for white on the selected square.
  2. 2.Count the clue square plus every touching orthogonal and diagonal neighbor inside the board.
  3. 3.Give all sixteen cells a final color and match every clue; the clean checker solution scores 840.

About Mosaic Puzzle

Mosaic Puzzle is a compact four by four version of the neighborhood-counting logic puzzle also known as Fill-a-Pix. Every square carries a number. That clue tells you exactly how many black squares appear in the clipped three by three neighborhood centered on it. The clue square itself counts, as do all orthogonal and diagonal neighbors that remain inside the board.

Simon Tatham's maintained Mosaic documentation supplies the principal rule reference, while Fill-a-Pix.net independently cross-checks the same self-inclusive neighborhood behavior. The alternating checker fixture, its sixteen clues, controls, contradiction display, and scoring are Lizely product choices. The fixed board makes every action and expected count reproducible.

Use the arrow keys to move the visible selection. Press Space to mark the current square black. Press Enter to mark it white. Pressing the same key on an already matching square returns it to unknown; choosing the other color replaces the previous mark. Mouse and touch users can click for black and use the context-menu gesture for white.

Neighborhood size changes at the board edge. A corner clue sees four squares: itself, two orthogonal neighbors, and one diagonal neighbor. A non-corner edge clue sees six squares. An interior clue sees all nine cells of a complete three by three area. The small count printed at the lower-right of every square shows the current black total beside the required clue.

The disclosed answer alternates black and white like a checkerboard. Zero-based black cells are 0, 2, 5, 7, 8, 10, 13, and 15; the other eight cells are white. Its clue rows are 2-3-3-2, 3-5-4-3, 3-4-5-3, and 2-3-3-2. Marking all sixteen cells correctly completes the puzzle in sixteen actions and scores 840 from a starting score of 1,000.

Validation runs after every mark. For each clue, the browser calculates the black cells already present and the unknown cells that could still become black. A contradiction is reported if the black count already exceeds the clue or if black plus unknown can no longer reach the clue. This catches both overfilling and marking too many required candidates white without revealing the solution.

Completion requires every square to have a final black or white state and every clue to equal its exact black count. The independent test fixture verifies self-inclusion, diagonal inclusion, corner, edge and interior neighborhood sizes, binary coverage of all sixteen squares, eight checker cells, both contradiction directions, and the complete sixteen-action keyboard simulation with final score.

The board is a semantic CSS grid rather than a canvas. Every button announces its row, column, clue, mark, and selection state. All colors, borders, surfaces, warnings, and focus outlines use the site's CSS variables. There is no image download, random service, audio, timer, account, hardware access, or pointer-only action.

Restart restores sixteen unknown cells, the first cursor, score, and status. A completed best score may be stored only in this browser's localStorage. Double-press Escape for the shared simulated spreadsheet boss screen, then repeat the gesture to resume the unchanged puzzle. For related deduction games, try LITS, Stitches, Heyawake, or Hitori.

Methodology & sources

For each of 16 cells, the logic enumerates in-bounds row and column offsets from −1 through 1, including the clue cell. It counts black marks and unknown candidates. Deadlock means black exceeds the clue or black plus unknown is below it. Completion requires 16 non-overlapping black/white marks and exact counts. Score is max(0, 1000 − 10×mark actions).

Frequently asked questions

Does a clue count its own square?
Yes. The clue cell is the center of its neighborhood and counts if it is black.
How many cells does a corner clue count?
Four: the corner itself, two side neighbors, and one diagonal neighbor.
Why does the game report a contradiction before the board is full?
A clue is impossible when it already has too many black cells or too few unknown candidates left to reach its number.
Is the puzzle random?
No. It uses a disclosed four by four checker fixture so every clue and completion action can be tested exactly.

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