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