Cat sudoku rules: how to play Catzzle

Place one cat in every color region, and only one, so that no two cats share a row, a column, or a corner.

1. Exactly one cat in each color region.
2. Exactly one cat in each row and in each column.
3. No two cats may touch, not even diagonally.
4. Some cats are already placed when the puzzle starts. They are part of the solution and cannot be moved.

A board with N rows has N columns, N color regions and N cats in its solution: five on a 5×5 board, ten on a 10×10.

1. Tap a square once to mark it with an X, meaning no cat can go there.
2. Tap it again to place a cat.
3. Tap a third time to clear the square.

You have three lives per puzzle. If you place a cat on a square where it does not belong, the game refuses it and you lose a life. After three wrong cats the puzzle starts again with full lives, so it pays to place a cat only when you are sure.

Look for the smallest color region. A region of one square must hold a cat, so place it straight away. That cat rules out its whole row, its whole column, its region and the eight squares around it; mark them all with X. Now check every row, column and region for one that has a single open square left. That square is the next cat. Most early boards solve with nothing more than this loop.

Boards start at 5×5 and gain a row and column as you climb: 6×6 from level 11, 7×7 from level 26, 8×8 from level 51, 9×9 from level 101 and 10×10 from level 251.