GridMew1Exclude common neighbors
The cat in row 2 must occupy one of row 2, column 1; row 2, column 2; row 2, column 3. Each of row 3, column 2 touches every candidate, so none can hold a cat.
Before step 1. Exclude 1 cells; then scan for a new single.Puzzle gm-8-0012
8 × 8 challenge
Take this puzzle one clear step at a time.
Try the puzzle yourself, then explore how the deductions build.
Puzzle board · starting state
Your starting point
This original 8×8 board has 8 connected regions and 2 fixed cats. The smallest region is H, with 3 cells. Start by ruling out every other cell in each fixed cat’s row, column and region, plus its immediate neighbors.
The verified route below uses 6 forced placements and 6 candidate-elimination steps after the givens. Region sizes: A: 12 · B: 5 · C: 11 · D: 13 · E: 8 · F: 7 · G: 5 · H: 3. These are observations about this board, not a guarantee that a smaller region always contains the next move.
Read each diagram in sequence. Cats and × marks in the before-state come from earlier deductions. Green outlines identify the current observation. Open the final answer only when you want the spoiler.
Step-by-step walkthrough
2Use a candidate lock
Every candidate in region B lies in row 2 (row 2, column 1; row 2, column 2). Its cat must use that shared section. Exclude row 2, column 3 from the rest of row 2.
Before step 2. Exclude 1 cells; then scan for a new single.3Exclude common neighbors
The cat in row 2 must occupy one of row 2, column 1; row 2, column 2. Each of row 3, column 1 touches every candidate, so none can hold a cat.
Before step 3. Exclude 1 cells; then scan for a new single.4Use a candidate lock
Every candidate in row 3 lies in region C (row 3, column 3; row 3, column 4; row 3, column 5). Its cat must use that shared section. Exclude row 4, column 4; row 4, column 5 from the rest of region C.
Before step 4. Exclude 2 cells; then scan for a new single.5Use a candidate lock
Every candidate in region G lies in row 7 (row 7, column 2; row 7, column 3). Its cat must use that shared section. Exclude row 7, column 1; row 7, column 4; row 7, column 5 from the rest of row 7.
Before step 5. Exclude 3 cells; then scan for a new single.6Exclude common neighbors
The cat in row 7 must occupy one of row 7, column 2; row 7, column 3. Each of row 6, column 2; row 6, column 3 touches every candidate, so none can hold a cat.
Before step 6. Exclude 2 cells; then scan for a new single.7Check region F
region F has only one remaining candidate: row 6, column 4. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 7. Place one cat, then exclude 8 other cells.8Check row 7
row 7 has only one remaining candidate: row 7, column 2. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 8. Place one cat, then exclude 3 other cells.9Check row 2
row 2 has only one remaining candidate: row 2, column 1. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 9. Place one cat, then exclude 2 other cells.10Check row 5
row 5 has only one remaining candidate: row 5, column 7. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 10. Place one cat, then exclude 1 other cells.11Check row 4
row 4 has only one remaining candidate: row 4, column 3. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 11. Place one cat, then exclude 1 other cells.12Check row 3
row 3 has only one remaining candidate: row 3, column 5. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 12. Place one cat, then exclude 0 other cells.Show solution · reveals all cat positions
The final cats satisfy every row, column and region quota, with no edge or corner contact.
Cat positions: r1c6, r2c1, r3c5, r4c3, r5c7, r6c4, r7c2, r8c8.