Original puzzle gm-8-0002
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 three givens leave row 5 with r5c6 and r5c8, both in E. Keep that pair open and remove E’s candidates from row 4. This makes a single without guessing which edge cell wins.
8×8 · 3 fixed cats · 6 explained deductions. Region sizes: A: 6 · B: 6 · C: 15 · D: 8 · E: 13 · F: 5 · G: 5 · H: 6.
The row-5 lock removes r4c6 and r4c8. Row 4 then forces r4c5, and its neighborhood eliminates r5c6.
r4c8 need not touch both row-5 choices. It is excluded because E’s required cat is already reserved for row 5.
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.
C B B B A A A A C B B B D D A A C C D D D D E E C C C D D E E E C C C C C E E E C C C F E E E E H H H F F G G E H H H F F G G G
Fixed cats: row 7, column 7; row 6, column 4; row 3, column 1. One cat is required in each row, column and region.
Every candidate in row 5 lies in region E (row 5, column 6; row 5, column 8). Its cat must use that shared section. Exclude row 4, column 6; row 4, column 8 from the rest of region E.
Before step 1. Exclude 2 cells; then scan for a new single.row 4 has only one remaining candidate: row 4, column 5. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 2. Place one cat, then exclude 4 other cells.row 5 has only one remaining candidate: row 5, column 8. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 3. Place one cat, then exclude 2 other cells.row 2 has only one remaining candidate: row 2, column 3. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 4. Place one cat, then exclude 3 other cells.row 1 has only one remaining candidate: row 1, column 6. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 5. Place one cat, then exclude 0 other cells.row 8 has only one remaining candidate: row 8, column 2. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 6. 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: r1c6, r2c3, r3c1, r4c5, r5c8, r6c4, r7c7, r8c2.
gm-8-0008 · 8×8 · challenge
Practice candidate locks on another 8×8 board.
Read this walkthrough →gm-6-0015 · 6×6 · challenge
Transfer candidate locks to a 6×6 grid; compare how the candidates change.
Read this walkthrough →gm-8-0006 · 8×8 · intro
Compare this route with single-candidate placements, and check why that different rule is needed.
Read this walkthrough →
GridMew