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