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