Click any cell to shade it (dark) or unshade it. Three rules must be satisfied:
1. No repeats unshaded: In every row and column, no number may appear more than once among the unshaded cells.
2. No touching shaded cells: Two shaded cells may never share an edge (diagonal is fine).
3. All unshaded cells connected: Every unshaded cell must be reachable from every other unshaded cell by moving horizontally or vertically through unshaded cells.
Right-click or long-press to place a circle dot — use these as notes to mark cells you're certain should NOT be shaded. Hitori was popularised by Nikoli (Japan).