1. Start with the smallest colored regions
Small regions carry the most information. If a two-cell region sits across two rows, each possible cat may block a different diagonal. Mark those consequences before looking elsewhere. Large regions often become easy only after smaller regions have claimed their rows and columns.
2. Count legal cells, not empty cells
An empty square is not automatically possible. A useful scan ignores cells blocked by an existing cat’s row, column, region, or diagonal. When only one legal cell remains in a line or region, that cat is forced.
3. Use line pressure
Suppose every legal cell for a colored region lies in the same row. The region’s cat must occupy that row, even if you do not yet know the exact column. Therefore every cell outside that region in the same row can be marked X. The same logic works with columns.
4. Mark diagonals immediately
The diagonal rule creates many avoidable mistakes. After every confirmed cat, mark the four corner-touching cells before making another move. On the edge or in a corner there are fewer neighbors, which can make those placements especially powerful.
5. Look for region pairs
If two regions can only place their cats in the same two rows, those rows are reserved for those regions. Other regions cannot use those rows. This pair logic is similar to a locked pair in regular Sudoku, but it operates across irregular shapes.
6. Alternate between regions and lines
Do not scan only by color. A region deduction creates row pressure; a row deduction creates column pressure; a column deduction may collapse another region. Strong solving is a loop: region, row, column, diagonal, then back to region.
7. Use contradiction carefully
When direct deductions stop, test one of two remaining cells mentally. Follow its immediate row, column, region, and diagonal consequences. If the assumption leaves another region with no legal cell, the tested square is impossible. Mark it X, but avoid long speculative chains that are hard to audit.
8. Treat the hint as a lesson
After a hint reveals a cat, do not rush onward. Ask which constraint made that position inevitable. Then mark every cell the cat blocks. A hint is most useful when it teaches the deduction you missed.
A practical scan order
- Regions with one or two legal cells.
- Rows with one or two legal cells.
- Columns with one or two legal cells.
- Diagonal neighbors around every confirmed cat.
- Locked region pairs across two rows or columns.
- A short contradiction test only after all direct scans.
Common mistakes
Most errors come from forgetting that diagonal contact is illegal, counting visually empty cells as legal, or placing a cat because it “looks right.” Every placement should have a reason you can state in one sentence. If you cannot name the row, column, region, pair, or contradiction that forces it, keep the square marked as a candidate instead.
Tips by difficulty
Cozy boards usually yield to small-region scans and immediate diagonal marks. Clever boards need repeated line pressure. Tricky boards add locked pairs and short contradiction checks. The rules never change; only the number of deductions between forced placements grows.
Put the strategy into practice
Open today’s board and follow the scan order from the top. If a rule is unclear, keep the rules page beside the puzzle.