Meowdoku! Three-Cell Line Rule: How to Cross Out the Middle

When a single color region in Meowdoku! forms a straight line of exactly three consecutive cells, you can immediately place an X on the squares directly flanking the middle cell in the adjacent parallel lanes. You do not need to know which of the three cells contains the cat.

How the Three-Cell Deduction Works

In Meowdoku!, each row, column, and color region contains exactly one cat. Cats cannot touch one another orthogonally or diagonally across corners.

When a color region is confined to a straight line of three cells within a single column, its cat must occupy the top, middle, or bottom cell. Every possible placement touches the middle cell's direct orthogonal neighbors in adjacent columns:

• Top cell: Touches the flanking squares diagonally.
• Middle cell: Touches the flanking squares orthogonally.
• Bottom cell: Touches the flanking squares diagonally.

Because those adjacent squares border every legal placement within the three-cell strip, neither can ever contain a cat.

Steps to Apply the Deduction

Follow these steps whenever a straight three-cell territory appears on the board:

1. Confirm that the three consecutive cells belong to the same color region and form a straight line without turns.
2. Identify the single center cell of the three-cell line.
3. Check the adjacent squares perpendicular to that center cell.
4. Mark an X on both neighboring squares if they lie within the puzzle boundaries and are currently unmarked.

In a horizontal three-cell strip, the same geometric logic applies vertically. The squares directly above and below the center tile fall within the cat's reach from the left, middle, or right positions, making both flanking spaces safe to eliminate.

Boundary Limits and Formation Errors

Before placing Xs with this rule, verify that the board state meets all three requirements:

• Odd-length center required: Do not apply this rule to a four-cell line. A four-cell straight line has two middle cells rather than a single center point, so neither individual row or column is covered by all four possible placements.
• Grid boundaries: If a vertical three-cell strip sits against the outer border (such as Column 1), only the inward flanking square in Column 2 exists to receive an X.
• Single region boundary: Ensure all three consecutive squares belong to the exact same color territory. If the line crosses a boundary between two different color regions, the shared contact deduction does not hold.