X-Wing: Advanced Solving Sudoku Technique


X-Wing by createclassicsudoku.com , and www.kristanix.com , and humage.com , and hodoku

X-Wing:

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.

or

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.

Candidate Numbers (or Candidate Values) of an blank/empty square is a list of 'possible values' or candidates for this blank/empty cell.

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 step-by-step style

Above is an example of using DoubleRowsOneDigitCheck(a.k.a. one case of X-Wing) 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 convenience, 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?

 

 

 

Solving Sudoku Methods Explained

This article answers questions: What are commonly used solving sudoku methods? What solving Sudoku methods do we use? In what sequences?

Basic Solving Sudoku Method: One Choice

a.k.a Sole Candidate, Only Candidate, or Naked Single

Basic Solving Sudoku Method: Elimination

a.k.a Hidden Single, Loner

Advanced Solving Sudoku Method: Subset2

a.k.a Pair, Naked Pair, or Naked Twins

Advanced Solving Sudoku Method: SubsetPosition2

a.k.a Hidden Pair or Hidden Twins

Last updated 3 mins ago

Advanced Solving Sudoku Method: Interaction

a.k.a Box/Row Claim or Intersection , or Locked Candidates

Solving Sudoku Methods Explained

This article answers questions: What are commonly used solving sudoku methods? What solving Sudoku methods do we use? In what sequences?