Solving/Creating Sudoku Techniques

Methods that used to solve Sudoku puzzles are also used to create them.


http://www.createclassicsudoku.com


Basic Solving Sudoku Technique - OneChoice

Author: Y Zheng, Published: 02/10/2017

The most basic solving Sudoku technique is OneChoice (we call it as OneChoice in http://www.createclassicsudoku.com).

You are given a Sudoku puzzle with one and only one solution, and your task is to fill the blank squares with numbers 1-9 so that each number 1-9 appear once and only once in each row, column, and box.

OneChoice is the most basic solving Sudoku technique. Once you find that only one number can be filled in a blank square because all other numbers already appear in its row, column, or box, we can fill this number to the empty square.






Basic Solving Sudoku Technique - Elimination (Row-Elimination, Column-Elimination, Box-Elimination)

Author: Y Zheng, Published: 02/10/2017



You are given a Sudoku puzzle with one and only one solution, and the task is to fill the blank squares with numbers 1-9 so that each number 1-9 appear once and only once in each row, column, and box.

One of the most basic solving Sudoku techniques is Elimination (we call it as Row-Elimination, Column-Elimination, and Box-Elimination in http://www.createclassicsudoku.com). Once you find that in a mini-box (or row or column), a number can only go to one empty square because all other empty squares cannot take this number, we can fill it into the empty square.

Box-Elimination is one of the most basic solving Sudoku technique. Once you find that in a mini-box (or row or column), a number can only go to one empty square because all other empty squares cannot take this number, we can fill it into the empty square. Box-Elimination - In a mini-box (or row or column), a number can only go to one empty square because all other empty squares cannot take it.



Advanced Solving Sudoku Technique - Subset (Subset2Row/Subset2Col/Subset2Box, Subset3Row/Subset3Col/Subset3Box, Subset4Row/Subset4Col/Subset4Box)

Author: Y Zheng, Published: 02/10/2017



You are given a Sudoku puzzle with one and only one solution, and the task is to fill the blank squares with numbers 1-9 so that each number 1-9 appear once and only once in each row, column, and box.

One advanced solving Sudoku techniques is Subset (we call it as Subset2Row/Subset2Col/Subset2Box, Subset3Row/Subset3Col/Subset3Box, Subset4Row/Subset4Col/Subset4Box in http://www.createclassicsudoku.com). Once you find that in a row (or column or box), two empty squares together share same candidate numbers, then we know that these two numbers in this row will be in these two empty squares. Therefore, we can remove these two numbers from other empty squares in this row (or column or box). We call this method Subset2Row (or Subset2Col or Subset2Box).

When solving a Sudoku puzzle, we mark possible numbers for an empty square. These possible numbers are called candidate numbers. If numbers 1, 3, 4 are the numbers that are not yet shown in an empty square's row, column, or box, we call {1, 3, 4} as the empty square's candidate numbers.

When three empty squares in a row (or column or box) together contain three candidate numbers, these three numbers will be only in these three empty squares, therefore we can remove these three numbers from other empty squares in this row (or column or box). We call this method Subset3Row (or Subset3Col or Subset3Box).

When four empty squares in a row (or column or box) together contain four candidate numbers, these four numbers will be only in these four empty squares, therefore we can remove these four numbers from other empty squares in this row (or column or box), and we call it Subset4Row (or Subset4Col or Subset4Box).



Advanced Solving Sudoku Technique - SubsetPosition (SubsetPosition2Row/SubsetPosition2Col/SubsetPosition2Box, SubsetPosition3Row/SubsetPosition3Col/SubsetPosition3Box, SubsetPosition4Row/SubsetPosition4Col/SubsetPosition4Box)

Author: Y Zheng, Published: 02/10/2017



You are given a Sudoku puzzle with one and only one solution, and the task is to fill the blank squares with numbers 1-9 so that each number 1-9 appear once and only once in each row, column, and box.

One advanced solving Sudoku techniques is SubsetPosition (we call it as SubsetPosition2, SubsetPosition3, SubsetPosition4 in http://www.createclassicsudoku.com). Once you find that in a row (or column or box), two untaken numbers only appear in two empty squares, then these two empty squares will be these two numbers. Therefore, we can remove all other candidate numbers from these two empty squares. We call this method SubsetPosition2Row (or SubsetPosition2Col or SubsetPosition2Box).

When solving a Sudoku puzzle, we mark possible numbers for an empty square. These possible numbers are called candidate numbers. If numbers 1, 3, 4 are the numbers that are not yet shown in an empty square's row, column, or box, we call {1, 3, 4} as the empty square's candidate numbers.

Once you find that in a row (or column or box), three untaken numbers only appear in three empty squares, then these three empty squares will be these three numbers. Therefore, we can remove any other candidates from these three squares. We call this method SubsetPosition3Row (or SubsetPosition3Col or SubsetPosition3Box).

Once you find that in a row (or column or box), four untaken numbers only appear in four empty squares, then these two empty squares will be these four numbers. Therefore, all other candidates can be removed from these four empty squares. We call this method SubsetPosition4Row (or SubsetPosition4Col or SubsetPosition4Box).



Advanced Solving Sudoku Technique - Interaction (InteractionRowBox/InteractionColBox, InteractionBoxRow/InteractionBoxCol)

Author: Y Zheng, Published: 02/10/2017



You are given a Sudoku puzzle with one and only one solution, and the task is to fill the blank squares with numbers 1-9 so that each number 1-9 appear once and only once in each row, column, and box.

One advanced solving Sudoku techniques is Interaction (we call it as InteractionRowBox, InteractionColBox, InteractionBoxRow, InteractionBoxCol in http://www.createclassicsudoku.com).

InteractionRowBox - In a row, a number only goes to columns within a mini-box. We can eliminate the possibility of this number in other empty squares in this mini-box.

InteractionColBox - In a column, a number only goes to rows within a mini-box. We can eliminate the possibility of this number in other empty squares in this mini-box.

InteractionBoxRow - In a box, a number only goes to squares within a row. We can eliminate the possibility of this number in other empty squares in this row.

InteractionBoxCol - In a box, a number only goes to squares within a column. We can eliminate the possibility of this number in other empty squares in this column.



Advanced Solving Sudoku Technique - X-Wing (DoubleRowsOneDigitCheck/DoubleColsOneDigitCheck, TripleRowsOneDigitCheck/TripleColsDigitCheck)

Author: Y Zheng, Published: 02/10/2017



You are given a Sudoku puzzle with one and only one solution, and the task is to fill the blank squares with numbers 1-9 so that each number 1-9 appear once and only once in each row, column, and box.

One advanced solving Sudoku techniques is X-Wing (we call it as DoubleRowsOneDigitCheck, DoubleColsOneDigitCheck, TripleRowsOneDigitCheck, TripleColsDigitCheck in http://www.createclassicsudoku.com).

DoubleRowsOneDigitCheck - In two rows, a number will be in two columns (forms a X-wing for the two possibilities), this number can be removed from other empty squares in these two columns.

DoubleColsOneDigitCheck - In two columns, a number will be in two rows (forms a X-wing for the two possibilities), this number can be removed from other empty squares in these two rows.

TripleRowsOneDigitCheck - In three rows, a number will be in three columns, this number can be removed from other empty squares in these three columns.

TripleColsOneDigitCheck - In three columns, a number will be in three rows, this number can be removed from other empty squares in these three rows.



Advanced Solving Sudoku Technique - XY-Wing (xywingRowBox/xywingColBox)

Author: Y Zheng, Published: 02/10/2017



You are given a Sudoku puzzle with one and only one solution, and the task is to fill the blank squares with numbers 1-9 so that each number 1-9 appear once and only once in each row, column, and box.

One advanced solving Sudoku techniques is xy-Wing (we call it as xywingRowBox, xywingColBox in http://www.createclassicsudoku.com).

xyWingRowBox - If a common friend causing two empty squares (one square is in the same row as this common friend, another one is in the same box as this common friend), one of them has to filled with a number, we can remove this number from the common friends of this two empty squares.

xyWingColBox - If a common friend causing two empty squares (one square is in the same column as this common friend, another one is in the same box as this common friend), one of them has to filled with a number, we can remove this number from the common friends of this two empty squares.


Expert Solving Sudoku Technique - Guessing (conflictElimination)

Author: Y Zheng, Published: 02/10/2017



You are given a Sudoku puzzle with one and only one solution, and the task is to fill the blank squares with numbers 1-9 so that each number 1-9 appear once and only once in each row, column, and box.

One expert solving Sudoku techniques is Guessing (we call it as GuessElimination). http://www.createclassicsudoku.com).

If we guess an empty square to be a number, and we found there is a conflict (e.g., two same numbers in a row/column/box or an empty square has ZERO candidate numbers). then we can remove these guessed number from the empty square's candidate numbers. We call this method GuessElimination