Cat Sudoku on Plainoku uses three placement rules: one cat in every row, column and colored region, with no touching cats. These are Queens-style logic puzzles, not classic number sudoku.
You leave most squares empty. The task is to find a complete arrangement of cats that satisfies all the constraints together. Understanding what each rule excludes is more useful than trying to match the board to familiar three-by-three sudoku boxes.
What are the three Cat Sudoku placement rules?
- Place exactly one cat in every row and every column.
- Place exactly one cat in every colored region.
- No two cats may touch along an edge or at a corner.
All three conditions apply at once. A cat can have a different color from another cat and still conflict because they share a row. Two cats in different rows and columns can still conflict because their squares touch diagonally. Check the full relationship between placements, rather than one feature at a time.
Why does each row and column need exactly one cat?
Rows run horizontally; columns run vertically. Once a cat occupies a row, every other square in that row is unavailable to another cat. The same applies to its column, even if the other square is far away or belongs to a different region.
On a 5×5 board, five rows require five cats. The column rule then requires those cats to occupy five different columns. If one column has two cats, another column cannot receive its required cat without increasing the total. Use both directions when checking the board: completing all rows alone is not enough.
How do colored regions change Cat Sudoku?
Each color marks a connected region that needs one cat. Its shape can be narrow, irregular or spread across several rows and columns. The borders show where a region ends. There is no requirement for a region to be a square, or for every region to have the same number of cells.
A cat fills its entire region's quota, not just its immediate neighborhood. Another cat at the opposite end of that region would still conflict. Conversely, sharing a border does not make two regions the same region. Inspect the color and boundary together, especially where several small regions meet.
Does “no touching” mean a full chess diagonal?
No. Touching means that two squares share an edge or corner. A cat can exclude up to eight neighboring squares: left, right, above, below, and the four diagonal neighbors that exist on the board. At an edge or corner, fewer neighbors exist.
Queens-style here does not mean that cats attack along an unlimited chess diagonal. A cat at row 2, column 2 touches row 3, column 3, but does not touch row 4, column 4. That farther square must still pass the row, column and region checks. A different color never overrides the no-touching rule.
Which pairs of Cat Sudoku placements conflict?
Coordinates count rows from the top and columns from the left. These examples compare two cats; a full solution must also leave suitable positions for every remaining row, column and region.
Scroll the examples table horizontally on smaller screens.
| Two cat positions | Region condition | Result |
|---|---|---|
| R2C2 and R2C5 | Different regions | Conflict: same row |
| R1C4 and R4C4 | Different regions | Conflict: same column |
| R2C2 and R3C3 | Different regions | Conflict: touching corners |
| R2C2 and R4C4 | Different regions | No conflict between this pair |
| R1C1 and R5C5 | The same region | Conflict: region already occupied |
Is a legal placement always part of the answer?
A placement can satisfy every rule against the cats currently on the board and still prevent a complete solution. For example, it might use a column that another region will eventually need. The absence of a red warning tells you about current conflicts, not the outcome of every future choice.
Before committing, ask what remains available in each affected unit. If a row, column or region would have no possible home, revisit the placement or the notes that excluded its alternatives. The scanning guide and only-possible-square guide help turn this check into a deduction.
How are board sizes and complete solutions checked?
Easy, Medium, Hard, Expert and Master correspond to 5×5, 6×6, 7×7, 8×8 and 9×9. They name board sizes, not calibrated logical difficulty ratings. You can open any size without unlocking it. Each generated Plainoku puzzle is checked for exactly one valid complete solution and connected color regions.
Completion requires the board's number of cats with no conflicts. Crosses are not part of that check, and you do not need to fill the empty squares. Read how to use the controls or how to record exclusions, then try the rules on a 5×5 Cat Sudoku board.