数独天下

fill in the digits in the grids, make each rows, each columns and each n-grids filled with digits from 1 to n(4,6,9)

Feature:
three grid type:4x4 grid,6x6 grid,9x9 grid 
four difficulties:beginner,simple,medium and hard
hint will tell you the resolve details
one key notes
three skins
state saving function allow you continue to play