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