How to play Sudoku

The Sudoku is played over 9x9 grid, in each row
there are 9 slots, some of them are empty and need to be filled

• Each row, column and grid must contain the numbers 1 to 9
• A number can appear only once on each row
• A number can appear only once on each column
• A number can appear only once on each area (3*3 grid)
  

The bottom line : A number should appear only once on row, column or grid.
However above all the ultimate challenge behind it is doing it fast!
Apparently there are 6,670,903,752,021,072,936,960 possible games!

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