• make board
  • implement using flat array
• select, fill
• validtion, highlight errors
  • row
  • col
  • rect
• persistence
• check solution
  • generator sometimes create boards with a lot of clues
• UI
  • colored numbers
  • dim not current numbers
  • fix numbers
  • better numpad (show fillingness of a number)
  • better checkbox UI
  • use SVG for the board
• keyboard navigation
  • prevent keyboard from checkboxes
• corner hints
• implement solver and generator sudoku
• difficulty levels
• undo / redo
• timer