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.
8
7
3
6
9
5
5
4
1
6
4
8
8
6
7
9
3
2
3
9
1
8
2
8
7
5
*** Hard