# Rules

Sudoku is played on a grid that consist of 9x9 spaces arranged in 9 rows (placed horizontally) and 9 columns (placed vertically) grouped into squares with 3x3 size.

Every row, column and square (9 spaces each) must be filled with numbers from 1 to 9, without duplicating a number on the same row, column or square.

At the beginning of the game, in some of the cells on the grid, there are arranges some numbers. The game goal is to fill all the blank squares with the numbers from 1 to 9. The more numbers the Sudoku grid has at the beginning of the game, the easier is the Sudoku puzzle. The difficult Sudoku puzzles have only few filled with numbers grids at the beginning of the game, but the most difficult puzzles have only 17 numbers.

There is only one condition – Every row, every column and each of the little squares in size 3x3, after the filling must contain all numbers from 1 to 9. Moreover each number can be present once in a given row, column or square.

Within a row, column or square from the grid, each number must appear only once in it.

✓Correct

✗Incorrect

You can find a lot of information on the internet about techniques for solving Sudoku puzzles. We won’t be covering all techniques for solving the Sudoku grid, instead we’ll give you initial direction. In the process of solving, everyone can choose the techniques that he/she likes for solving the Sudoku, also we have some techniques that we explained in our articles.

Do not repeat any numbers

As you can see in the upper left square (marked with blue) there are already filled 7 from 9 spaces. The only numbers missing in this square are 5 and 6. When we trace which numbers are missing from the square, row or column, we can exclude or use deduction to find out which number we should place in the empty fields.

For an example, in the upper left square we know that we should place 5 or 6 to complete the whole square, but we can’t tell which number where should be positioned before checking the nearby rows and columns. This means that we should ignore the upper left square and try to complete another part of the grid.

Do not try to guess

Sudoku is a logically based game, that’s why guessing won’t help. If you don’t know which numbers you have to place in particular space, keep checking the other parts of the grid until you see the opportunity to place a number. No need to rush- Sudoku is based on patience, inspiration and recognition of the patterns.

Use the process of exclusion

What does it mean “process of exclusion” while playing Sudoku? Here’s an example. In the Sudoku grid (shown below), in the left vertical column (marked with blue) are missing few numbers: 1, 5 and 6.

One of the ways to find out what number in which column to place using the ”process of exclusion” when you check the numbers that are already included in every square - because there can’t be duplicated numbers in a square, row or column.

In that case you can easily notice that number 1 is found in the upper left square and in the upper middle square (the numbers circled in red). This means that there’s only one place where you can put number 1 - in the square marked in green.  Thus the “process of exclusion” in Sudoku works – look carefully which spaces are clear, which numbers are missing and then by deduction, based on the positions of the numbers in the grid, you can find which numbers you must place.

The Sudoku rules are not difficult in general, but the game has endless options with millions of combinations and a wide variety of difficult levels. All of this is based on simple principles using the numbers from 1 to 9, where you have to fill the empty spaces, using logical thinking and the numbers shouldn’t be repeated in the same square, row or column.