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.Separate a regional reservation from a neighbor exclusion
Original puzzle gm-8-0012
By GridMew · Published 15 October 2026 · Updated 16 October 2026
8 × 8 challenge
Read the starting position, follow the deductions, and check the move that is easy to misread.
Puzzle board · starting state
How to approach this board
Coordinates such as r2c3 mean row 2, column 3. Count rows from the top and columns from the left.
The two far-apart givens leave a cluster of possibilities near the upper-left. Row 2 first excludes a common neighbor; B’s reservation then shrinks that row further. Keep the reasons in sequence.
8×8 · 2 fixed cats · 12 explained deductions. Region sizes: A: 12 · B: 5 · C: 11 · D: 13 · E: 8 · F: 7 · G: 5 · H: 3.
A deduction worth checking
Later, G has only r7c2 and r7c3. It reserves row 7, then its candidate pair excludes r6c2 and r6c3 by touching. These two operations prepare the first new cat.
A move to double-check · r2c3
B’s two candidates are in row 2. r2c3 is outside B, so it loses the row’s cat to that region; this is a quota argument, not a claim that B has one cell.
Green marks the cell being discussed, not a cat to place. This is the position before step 2; compare the deduction below.
Read the starting board as text
Each line is one row, left to right. Matching letters belong to the same connected region.
B B A A A A A A B B C A A C A A D B C C C C A A D D D C C C E E D D D D D C E E D D F F D C E E D G G F F F E E G G G F F H H H
Fixed cats: row 8, column 8; row 1, column 6. One cat is required in each row, column and region.
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.
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