# Sudoku

**Sudoku** is a game that looks like a number puzzle. Stimulates logical-mathematical reasoning and strategic thinking. At first it may seem very difficult, but you will see that with a little practice, knowing the right strategies, each day will become easier and more entertaining.

## Sudoku: how to play step by step 🙂

You will find a **huge square that is divided into several small squares**, and these small squares are grouped into middle squares. Each medium square has 9 small squares inside.

The aim of the game is to fill in the empty squares with numbers, so that:

- All lines (
**horizontal**) have all the numbers from 1 to 9, without repeating any. - All columns (
**vertical**) have all the numbers from 1 to 9, without repeating any. - All
**middle squares**they have all the numbers from 1 to 9, without repeating any.

## What is Sudoku?

In good Japanese, the name we all know is nothing more than a simplification of the phrase "**suji wa dokushin ni kagiru**", what does it mean "**numbers must be unique**"And it refers to a very simple numerical pastime of very simple instructions whose objective is to fill in all the empty boxes through an orderly numerical sequence. That requires logic and reasoning for the resolution.

## Sudoku History 🤓

Despite its name,** sudoku was not created in Japan**, the invention is attributed to the Swiss mathematician** Leonhard Euler. In the XVIII century**, created what he called "**latin squares**", a game in which the figures must appear only once in each row and in each column. **9 rows and 9 columns** became popular when **began to be published in the US**. In the 1970s.

It was there in** 1984**, when the Japanese **Maki Kaji met the game**. Upon returning to his homeland,** Kaji improved the game** (He gave the clue numbers, which already appear in the box, and created different degrees of difficulty, baptized it and turned it into a fever among his compatriots: today Japan has more than 600,000 magazines specialized in Sudoku.

**In the West, gambling went crazy in 2005**. The first step was taken in 1997, when the New Zealander **Wayne Gould visited Japan**, learned about Sudoku and developed a computer program for the game, released in 2004. 8 months ago, his creations of the game began to be published daily by The Times newspaper, which was soon followed by competition around the world.

## Sudoku Types

### Types of sudoku in addition to the conventional one:

**Diagonal:**To play, you must follow the same rules as traditional Sudoku, that is, complete all the squares using numbers from 1 to 9, without repetition in the horizontal and vertical lines. The most outstanding aspect of this sudoku puzzle is that, in addition to connecting the vertical and horizontal lines, you must make two central diagonals forming an X, with numbers from 1 to 9 and that they do not repeat themselves.**Irregular**: it has the same rules as the classic, except that the squares are irregular.**Kakuro:**Playing kakuro is not very difficult, although it is considered more complicated than sudoku. The objective is to place the numbers from 1 to 9 in such a way that they are not repeated in the sequence of the line and in the sequence of the column, being necessary that the sum of the numbers (horizontally or vertically) is equal to the related point .**Killer:**it is a combination of Sudoku and Kakuro. Therefore, there are demarcated areas where there can be no repeating numbers and whose sum must give the indicated value.**Megasudoku:**you should make the digits 1 through 12 appear only once in each row, column, and square. Similar to the traditional one but with three more numbers.**Minisudoku:**It differs from the traditional one by being composed of a smaller number of squares.**Multisudoku**: It is made up of several sudoku puzzles that together make up one.

## Tips to solve a Sudoku 🙂

The first thing to do to start solving Sudoku is **choose a format to guide** (row, column or square). If you don't pick just one and try to do everything at once, you can end up shuffling and confusing everything, which will take you much longer in the game.

Say, for example, you chose to start solving by lines. Then you will analyze the first horizontal line and see which numbers are already on it and which are missing. **Fill in the empty squares with the missing numbers,** paying attention to the numbers in the column to make sure it does not repeat itself.

After solving the first line, **go to the second line and repeat the process**. See what numbers you already have and which ones are missing to start filling in. If you don't have the number 1 on the second line, go to the first empty square and write 1. Then** look at the column for that square**. If the number 1 already exists in that column, remove it and write the 1 in another square. Remember to always check if you are not repeating any number that is already in the square.

Follow this rhythm to the end, and you can build your Sudoku game. In the end, it becomes more difficult to find a place that fits the numbers without repeating it, but anything is just trying to change the place numbers to make it easier.

## Sudoku: strategies 🤓

Here are some simple tips and strategies to help you solve a Sudoku puzzle.

### With Brands

Using marks, you can use these very simple (and even obvious) tips:

#### Single number

At any point, watch the game closely for cells that only have one number in the marks. This indicates that there is only one possibility for that cell.

#### Hidden number only

Often looking closely, you can find a "**hidden number only**". This number does not appear only in the marks. It is the only possible candidate in a row, column or 3x3 grid, it only appears in the middle of other numbers. See the image to the side:

In this image, you can see that the numbers 1 and 8 appear only once in their respective 3x3 grids. This indicates that they must necessarily be placed in those positions.

#### Single couple

1. If at any time you find the same pair of numbers only in the marks of a group (row, column or grid), it means that** this pair must necessarily appear in these two cells**. See the image below:

2. In this image we see that the numbers 1 and 3 appear alone in two cells, so they must be used in those cells. We just don't know what number goes in each cell. However, we know that the numbers 1 and 3 cannot appear in the other empty cells. Therefore, we only have one chance in each.

### No labels🤓

For those who do not want to use brands, we will explain a very simple and very useful strategy.

#### Crossed lines

The crossed lines technique is possibly **the first thing people learn when they play Sudoku**. Players learn by doing, because it is simple and basic.

In it, the player must choose a number (usually the one that is most present in the game) and draw imaginary lines on the lines and columns in which that number is present.

In the following example, we choose the number 9. We find all the places where it is present and we draw the imaginary lines on the lines and columns to indicate that the number 9 cannot be placed in those positions. Once this is done, we mark the free positions in green.

**Note** : It is important to note that some empty cells, although they were not eliminated by the imaginary lines, were not marked as free because they have the number 9 in the same 3x3 grid.

By analyzing the free positions, we can see that in the central 3x3 grid there is only one free position for the number 9, so we can place it in that position.

Once this is done, we repeat the process of the imaginary lines for the number that we have just placed. Check the result:

Newly** we must analyze the free positions in search of a new movement**. As we can see, in the lower central grid there is only one free position. Then we can put the number 9 and repeat the above procedure.

This time a single free position appeared in the lower left corner, so we put a 9 in that position and continued with the strategy.

Now we can see that we have four free positions for the number 9, none of which is unique in the 3x3 grid it is on. Therefore, we do not know where to place 9 using this strategy alone.

One possible way is **choose a new number and repeat this strategy just described**. You will probably be able to fill most of the cells using just this strategy.

Now that you have some strategies, have fun and exercise your brain by playing Sudoku.🙂

## Sudoku Rules

### Purpose of the game

Sudoku is a game that requires some time and thought, but once you know the rules, it becomes reasonably easy to play.

Sudoku generally **consists of a 9x9 table**, Which consists of **9 grids**, that have **9 cells respectively**.

The main idea of the game is that the player **you should fill the table with numbers from 1 to 9, without any repetition of numbers on the same line or grid.**

If you follow all these rules and manage to fill the table, then the game is won!

### Game strategy

Sudoku tables** were designed to have a single solution** And as such, it's normal that we don't get it right the first time.

For this same reason, most players prefer to write the numbers in pencil so that they can be erased if they have made a mistake.

### Reservations

Another suggestion to consider is the **use of trademarks**. By brands, we mean the **writing the various possibilities within each cell**. That is, if a cell can have the numbers 3 and 9, the ideal is to indicate (in small size) both numbers and solve the rest of the table, until the number corresponding to that cell is reached.

In some versions of Sudoku, these small marks are already included in the table, to facilitate their resolution. In these versions that already include marks, there are some tricks that will help you solve the puzzle:

**Single number**

Whenever in a Sudoku table (with marks) you find a number only in one cell, this is a** signal that there is only one possibility for that same cell**, that is, you must dial that number immediately in the cell.

### Hidden number only

Sudoku can sometimes be a complex game, but there are little tricks to help us figure out the game. For example, in games where there are brands, we sometimes find the so-called "**hidden number only**".

This number does not appear only in the cell (accompanied by other numbers), but it is the only possible candidate in a row, column, or 3x3 grid.

That is, when in a 3x3 grid, for example, the number 3 appears and does not appear in any other cell of that grid, then it is an indicator that the number 3 belongs to that same cell.

**Single couple**

As long as you find the same pair of numbers only in the marks of a 3x3 grid, then it means that this pair necessarily **must be present in these two cells**, the only question that arises here is which one will be in each one.

### No labels

If your version of Sudoku doesn't come with marks or if you don't want to use marks, there is another very simple strategy to help you master this game.

**Crossed lines**

The crossed lines technique is widely used, due to its great simplicity of use. Consists in **choose the number that appears most frequently in the whole table and draw** (with pencil so as not to be confused) **lines in the rows and columns to which that same number is associated.**

After we have drawn all the lines, we proceed to the stage of marking the cells that are not covered in those same lines. Then, it is analyzed which 3x3 grids do not have the number 9 and which have a space (not crossed out) to place it.

Once this is done, **choose another number and repeat that same strategy**, until all cells are filled. In the end, you need to check if there are repeating numbers on the same line or grid. If there are no repeating numbers, then the game is won.

### Play time and difficulty

**There is no maximum time for each Sudoku puzzle**, and each player can enjoy the game as long as they want.

A Sudoku game **can vary between 5 and 45 minutes**, but it all depends on the experience of the player and the level of difficulty of the game. Simply put, the more difficult the game, the more reasoning is needed, so the game will take longer.

As for the difficulty,** it is usually explicit in the title of the website or magazine**. There are easy games for beginners and very difficult for more experienced players. For experts, the most difficult levels can be really challenging, as the levels start to look very symmetrical, in which the numbers seem to be reflected. Therefore, in addition to the basic reasoning,** you also need a certain strategy.**

And so the article concludes. Congratulations! Now you know how to play Sudoku, or at least you have enough knowledge to solve these puzzles!

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