Sudoku

Controls:

• Click a cell to select it.
• 1-9: set a value in the selected editable cell.
• Shift+1-9 or Ctrl+1-9: toggle candidate marks.
• 0, Backspace, or Delete: clear selected editable cell.
• Arrow keys: move selection.
• R, N, or Enter: generate a new random puzzle.
• Optional mouse shortcut: click the same empty selected cell again to toggle candidates by 3x3 mini-position.