Original puzzle gm-8-0005
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.
Coordinates such as r2c3 mean row 2, column 3. Count rows from the top and columns from the left.
The two lower givens leave every column-5 candidate in E. Reserving E for that column removes its side branches. Watch the consequences in row 6 and columns 4 and 3 before placing any new cat.
8×8 · 2 fixed cats · 11 explained deductions. Region sizes: A: 4 · B: 4 · C: 4 · D: 9 · E: 24 · F: 8 · G: 7 · H: 4.
After four locks, row 1 can use r1c3 or r1c5. Both touch r2c4. Removing that shared neighbor finally forces r3c4 in column 4.
r6c4 is in E but outside column 5. The first lock excludes it through E’s quota, even though no exact column-5 position has been selected.
Green marks the cell being discussed, not a cat to place. This is the position before step 1; compare the deduction below.
Each line is one row, left to right. Matching letters belong to the same connected region.
A A A E E E E D B B A C E E E D B B C C E E E D E E C E E D D D F E E E E D D D F F E E E G G H F F E E G G G H F F F E G G H H
Fixed cats: row 7, column 6; row 8, column 8. One cat is required in each row, column and region.
Every candidate in column 5 lies in region E (row 1, column 5; row 2, column 5; row 3, column 5; row 4, column 5; row 5, column 5). Its cat must use that shared section. Exclude row 1, column 4; row 1, column 7; row 2, column 7; row 3, column 7; row 4, column 1; row 4, column 2; row 4, column 4; row 5, column 2; row 5, column 3; row 5, column 4; row 6, column 3; row 6, column 4 from the rest of region E.
Before step 1. Exclude 12 cells; then scan for a new single.Every candidate in row 6 lies in region F (row 6, column 1; row 6, column 2). Its cat must use that shared section. Exclude row 5, column 1 from the rest of region F.
Before step 2. Exclude 1 cells; then scan for a new single.Every candidate in column 4 lies in region C (row 2, column 4; row 3, column 4). Its cat must use that shared section. Exclude row 3, column 3; row 4, column 3 from the rest of region C.
Before step 3. Exclude 2 cells; then scan for a new single.Every candidate in column 3 lies in region A (row 1, column 3; row 2, column 3). Its cat must use that shared section. Exclude row 1, column 1; row 1, column 2 from the rest of region A.
Before step 4. Exclude 2 cells; then scan for a new single.The cat in row 1 must occupy one of row 1, column 3; row 1, column 5. Each of row 2, column 4 touches every candidate, so none can hold a cat.
Before step 5. Exclude 1 cells; then scan for a new single.column 4 has only one remaining candidate: row 3, column 4. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 6. Place one cat, then exclude 6 other cells.row 4 has only one remaining candidate: row 4, column 7. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 7. Place one cat, then exclude 1 other cells.row 5 has only one remaining candidate: row 5, column 5. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 8. Place one cat, then exclude 1 other cells.row 1 has only one remaining candidate: row 1, column 3. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 9. Place one cat, then exclude 1 other cells.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 10. Place one cat, then exclude 1 other cells.row 6 has only one remaining candidate: row 6, column 2. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 11. Place one cat, then exclude 0 other cells.The final cats satisfy every row, column and region quota, with no edge or corner contact.
Cat positions: r1c3, r2c1, r3c4, r4c7, r5c5, r6c2, r7c6, r8c8.
gm-8-0009 · 8×8 · challenge
Practice shared-neighbor exclusions on another 8×8 board.
Read this walkthrough →gm-6-0007 · 6×6 · challenge
Transfer shared-neighbor exclusions to a 6×6 grid; compare how the candidates change.
Read this walkthrough →gm-8-0012 · 8×8 · challenge
Compare this route with candidate locks, and check why that different rule is needed.
Read this walkthrough →
GridMew