SUDOKU
Write a number from 1 to 9 into each empty square in the grid so that every number from 1 to 9 appears exactly once in each horizontal row, each vertical column, and each 3×3 block.
7
5
6
1
9
8
3
1
5
3
2
6
5
7
9
6
2
7
1
8
4
3
8
2
5
*** Hard