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