Sudoku Puzzle (Free) app for iPhone and iPad

You won’t be looking for a paper puzzle ever again!
With 4 difficulty levels, intuitive interface, and all the functions right at your fingertips, this Sudoku app is sure to be your favorite. Interrupted? Exit Sudoku, and the puzzle is saved exactly as you see it!
* 4 levels - easy, medium, hard, extreme
* 3 input modes - digit first, cell first, popup
* Pencil marks with auto fill / erase, as specified in settings
* Auto-save
* Undo and Redo
* Intelligent hints
* Top scores and History
* Selected digit highlighting, as specified in settings
* Incorrect entry highlighting, as specified in settings
* Submit results and track progress online