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