Fill every cell with 0 or 1. No three of the same next to each other in a row or column, every row and column has as many 0s as 1s, and no two rows or two columns are the same. Tap a cell to cycle empty, 0, 1 (drag to paint). Keys: arrows move, 0 / 1 enter, Space cycles, Backspace clears, Z / Y undo and redo, H hint, C check, P pause.