Sudoku is played over a 9x9 grid.
1.each row must contain the numbers 1-9 exactly once each.
2.each column must contain the numbers 1-9 exactly once each.
3.each 3*3 sub grid must contain the numbers 1-9 exactly once each.
Click a number to choose the number, then click a blank cell to fill it. Click again to remove it.
The color of the number you filled is green (or yellow in night mode). While the number is finished all, its color becomes orange.