Fill every empty cell with a zero or a one so that each row and each column holds as many zeros as ones.

Never three alike side by side — not in a row, not in a column.

No two rows read the same, and no two columns do either.

Tap a cell for a zero, tap again for a one, once more to clear it. The digits the board came with stay put.

A reddish cell is one of three alike in a row, or a digit its row or column already has too many of; two lines that read the same are shaded too.

Learn the solving techniques