

Advanced Solving Sudoku Technique


XWing by us createclassicsudoku.com
, and
www.kristanix.com
, and
humage.com
, and hodoku


Take a look at these two possibilities of putting 5 in the fith row and the ninth row, aren't they form a Small shape of 'X'?These above two possibilites rule out the possiblity that number 5 could be in R3C5 and R4C8 in the fifth column and the eighth column. Therefore, we remove number 5 from R3C5 and R4C8. 

Hard Sudoku on 03/22/2018  
Solve Hard Sudoku on 03/22/2018 in a stepbystep style  
Above is an example of using DoubleRowsOneDigitCheck(a.k.a. one case of XWing) to refine the candidate values of R9C9 (the highlighted squares in the fifth column and the eighth column excluding those at the fith row and the ninth row). Blank/Empty Squares are marked with candidate values in red. 

In the fifth row and the ninth row, number 5 are confined to the fifth column and the eighth column. For the fifth row and the ninth row, let us check number 5.


For easy understanding, in our Sudoku solver, we call DoubleRowsOneDigitCheck: If in two rows all candidates of a certain digit are confined to two same columns, for these two columns this digit must appear within these two rows. DoubleColsOneDigitCheck: If in two columns all candidates of a certain digit are confined to two same rows, for these two rows this digit must appear within these two columns. 

How to find them?




Advanced Solving Sudoku Technique


XWing by us createclassicsudoku.com
, and
www.kristanix.com
, and
humage.com
, and hodoku


Take a look at these two possibilities of putting 5 in the fith row and the ninth row, aren't they form a Medium shape of 'X'?These above two possibilites rule out the possiblity that number 5 could be in R3C5 and R4C8 in the fifth column and the eighth column. Therefore, we remove number 5 from R3C5 and R4C8. 

Hard Sudoku on 03/22/2018  
Solve Hard Sudoku on 03/22/2018 in a stepbystep style  
Above is an example of using DoubleRowsOneDigitCheck(a.k.a. one case of XWing) to refine the candidate values of R9C9 (the highlighted squares in the fifth column and the eighth column excluding those at the fith row and the ninth row). Blank/Empty Squares are marked with candidate values in red. 

In the fifth row and the ninth row, number 5 are confined to the fifth column and the eighth column. For the fifth row and the ninth row, let us check number 5.


For easy understanding, in our Sudoku solver, we call DoubleRowsOneDigitCheck: If in two rows all candidates of a certain digit are confined to two same columns, for these two columns this digit must appear within these two rows. DoubleColsOneDigitCheck: If in two columns all candidates of a certain digit are confined to two same rows, for these two rows this digit must appear within these two columns. 

How to find them?





