I am glad to announce that we just release the v2.0 version of our Android game Ninja Sudoku which adds killer sudoku and the corresponding hint system.
If you would also try to play sudoku variant like Killer Sudoku, you are welcome to try it out. You can get it at:
https://play.google.com/store/apps/details?id=com.m00nlight.samuraisudoku
And any feedback or suggestion are welcomed
