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