Solving Classic Sudoku: 'X-Wing'

This is a very advanced sudoku solving technique. You need to have a great eye-sight to use this technique. If there is a number which can be placed only in two identical cells of different rows/columns, then that number cannot be placed in any other cell of the perpendicular columns/rows.

Take a look at this Classic Sudoku. Observe the 2nd and 6th rows.


In the 2nd row, '5' and '7' can only be placed in the cells marked in green. In the 6th row, '1' and '7' can only be placed in the cells marked in green.


The possible positions of '7' in the 2nd and 6th rows forms an x-wing and hence, '7' cannot be placed in any other cell of the perpendicular columns marked in red.


Using the '7' in R7C9, we find a unique position for '7' in the 7th box.

Other Solving Techniques

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