Sudoku Hard

Controls Pick a cell and enter 1–9 so every row, column and 3×3 box has each digit once. Conflicting digits turn red. ✎ (or N) is notes mode, ⌫ (or Delete) erases, arrow keys move. Undo (U, Z, Ctrl+Z), redo (Y) and auto notes (fills every empty cell with the candidates the rules allow) are available; the small number on each pad key is how many are left. The clock starts with your first entry and there is no pause.