Cat Zones › How to solve

How to solve Cat Zones puzzles

Seven techniques, from the ones you'll use on every board to the one that cracks the hardest 10×10. They work for any puzzle with the same rules (often called one-star Star Battle).

What are the rules again?

An n×n board is split into n colored zones. Place n cats so that every row, every column and every zone has exactly one cat, and no two cats touch, not even at a corner.

1. Start with the smallest zones

A zone of one cell must hold a cat, so place it immediately. Zones of two or three cells are almost as useful: their cat has very few places to go, and the techniques below usually pin it down within a few moves.

2. Clear everything a cat rules out

Once a cat is placed, mark X on its whole row, its whole column, every other cell of its zone, and the eight cells around it. Turn on Auto-mark X in the game to have these shown for you.

3. A zone locked inside one row or column

If every remaining cell of a zone lies in the same row, that row's single cat must belong to that zone. Every other cell in the row is empty. The same works for columns.

4. Count zones against rows

Extend technique 3 to groups: if two zones fit entirely inside the same two rows, those two rows already have their two cats, one for each zone. Every cell of any other zone in those rows is empty. Three zones inside three rows works the same way, and so do columns.

5. A row locked inside one zone

The reverse of technique 3: if every open cell left in a row belongs to one zone, that zone's cat is in this row. Cross out the rest of the zone everywhere else on the board.

6. Cells that would starve a zone

A cat removes all eight neighbors. If a cell touches every remaining cell of some zone (or sits in their row or column), a cat there would leave that zone with nowhere to go, so the cell must be empty. This often clears cells next to two- and three-cell zones.

7. Test a cell when you're stuck

Pick a cell with only a few alternatives and imagine a cat there. Apply techniques 2 to 6 in your head. If some row, column or zone runs out of open cells, the test failed, and the cell is definitely empty. Because every board has exactly one answer, this always moves you forward without guessing.

A routine that works

1. Place every forced cat (technique 1) and clear around it (technique 2).
2. Scan rows and columns for locked zones (techniques 3 to 5).
3. Look next to the small zones for cells that would starve them (technique 6).
4. Only then test a cell (technique 7).

Practice on the daily puzzle, or check a board you're stuck on with the solver.