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.
4
5
6
8
3
2
7
2
5
2
1
8
3
8
6
8
9
7
9
1
9
2
5
3
4
6
**** Very hard