Sudoku Mini is a great version of the classic puzzle but I'm not quite sure why it's called mini, apart from the obvious - it's on a mobile - reference.
Because Sudoku Mini is packed with all the features that you want from your Sudoku puzzles. There are various levels of difficulty, variable grid sizes and a built-in puzzle generator meaning you have literally billions of games to play.
Far better than an undo button. The puzzles are colourful and clear and it'll keep you entertained for as long as your journey to and from work lasts.