GridMew1Check region C
region C has only one remaining candidate: row 3, column 3. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 1. Place one cat, then exclude 14 other cells.Two singleton regions set up a vertical lock
Original puzzle gm-6-0003
By GridMew · Published 15 October 2026 · Updated 16 October 2026
6 × 6 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.
There are no givens. Regions C and F each contain one cell, at r3c3 and r6c6. After those forced cats, D still has a choice of rows, but both candidates occupy the leftmost column.
6×6 · 0 fixed cats · 7 explained deductions. Region sizes: A: 4 · B: 11 · C: 1 · D: 5 · E: 14 · F: 1.
A deduction worth checking
D can use r4c1 or r5c1. It therefore takes column 1’s cat, excluding r1c1 and r2c1 and leaving row 2 to resolve elsewhere.
A move to double-check · r2c1
Choosing the upper or lower D cell is unnecessary. Either choice would prevent r2c1, because column 1 can contain only one cat.
Green marks the cell being discussed, not a cat to place. This is the position before step 3; 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.
A A B B B B A A B B B B D D C B B B D E E E E E D E E E E E D E E E E F
Fixed cats: none. One cat is required in each row, column and region.
Step-by-step walkthrough
2Check region F
region F has only one remaining candidate: row 6, column 6. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 2. Place one cat, then exclude 9 other cells.3Use a candidate lock
Every candidate in region D lies in column 1 (row 4, column 1; row 5, column 1). Its cat must use that shared section. Exclude row 1, column 1; row 2, column 1 from the rest of column 1.
Before step 3. Exclude 2 cells; then scan for a new single.4Check row 2
row 2 has only one remaining candidate: row 2, column 5. 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.5Check row 1
row 1 has only one remaining candidate: row 1, column 2. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 5. Place one cat, then exclude 1 other cells.6Check row 4
row 4 has only one remaining candidate: row 4, column 1. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 6. Place one cat, then exclude 1 other cells.7Check row 5
row 5 has only one remaining candidate: row 5, column 4. Every other cell is excluded by earlier placements or deductions. Place the cat here.
Before step 7. 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: r1c2, r2c5, r3c3, r4c1, r5c4, r6c6.
Try another puzzle
A row lock can force a cat in the same row
gm-6-0012 · 6×6 · challenge
Practice candidate locks on another 6×6 board.
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gm-5-0014 · 5×5 · challenge
Transfer candidate locks to a 5×5 grid; compare how the candidates change.
Read this walkthrough →Two distant singleton regions supply the first anchors
gm-6-0028 · 6×6 · practice
Compare this route with single-candidate placements, and check why that different rule is needed.
Read this walkthrough →