Comfortable Sudoku'

Sudoku is a logic-based,number-placement puzzle. The objective is to fill empty grid with digits so that each column, each row, and each of the nine 3×3 block that compose the grid contains all of the digits from 1 to 9.

Comfortable Sudoku features:
★Press and hold a grid, you can enter a number directly.
☆15 different levels of difficulty
☆Three input modes
☆Undo / Redo
☆Hint mode