GridMewScan rows and columns together
Cross-check constraints instead of solving one region in isolation.
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Use one placement in several directionsCross-check a promising regionKeep a systematic orderApply the ideaOriginal exampleCheck your understandingOriginal GridMew lesson · Updated 16 October 2026
Learning goal: Alternate between regions and lines when the next forced placement is far from the last one.
Use one placement in several directions
A cat’s row and column are both full. Every other cell on those two lines can be excluded, even when it is far from the cat. That makes line scans different from the no-touch check, which affects only immediate neighbors.
Pick an unfilled row and inspect it from left to right. Ask which columns already contain cats, then which candidate regions are already filled, then which positions touch a cat. Repeat the process for an unfilled column.
Cross-check a promising region
Suppose a region spans two rows but one of those rows already has a cat elsewhere. All candidates in that row disappear from the region. You may now have a single candidate, or the remaining candidates may line up and create a region-line lock.
The specific board below records a verified forced step after two regional placements. Use the row and column labels in its diagram to reconstruct why other locations have disappeared. If a step follows earlier work, its preceding steps in the full walkthrough supply that context.
Keep a systematic order
Try rows first, columns second and regions third, then repeat after a placement. This is a way to organize attention, not a mathematical rule that rows must be solved first. A narrow region can be a better starting point when it immediately forces a cat.
A scan that finds no deduction is still useful: it shows which constraints have been checked. Avoid turning the absence of a single into permission to guess. Move on to candidate locks or read a staged hint.
Apply the idea to gm-6-0009
r2c3 means row 2, column 3, counting from the top left.
In gm-6-0009, first fill F at r6c1, then E at r5c6. The next useful observation is column 4, whose only candidate is r1c4. The route jumps to the top of the grid because constraints act along complete lines.
After that placement, r2c3 disappears through corner contact, while r1c2 and r1c3 disappear because row 1 is full. These updates help row 2 settle at r2c2. A line scan and a neighborhood scan cooperate; neither can replace the other.
A real step from gm-6-0009
column 4 has only one remaining candidate: row 1, column 4. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Check your understanding
After r1c4 is placed, which rule removes r2c3?
Show the explanation
Immediate corner contact: the cells differ by one row and one column. It is not a column-4 exclusion, because r2c3 is in column 3.