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