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