# Medium Sudoku puzzles

At the initial stage, each player gets acquainted with the rules and principles of the game and the available strategies, gets the first experience of achieving a winning result, regardless of the time it takes them to achieve it – quickly or significantly longer. Having familiarized with the principles, understanding the logic of the game interface and consolidating the results and speed of finding a solution on the first level, any user can go to the medium level online Sudoku, starting to improve their mathematical skills, logical reasoning and inference.

At the very beginning of the game, there is a 9x9 cell field consisting of nine rows (1x9) and nine columns (9x1) on the screen in front of each player. Some of the cells contain numbers. Only 1, 2, 3, 4, 5, 6, 7, 8, 9 are involved in the game. Also the visual field is divided into sectors (groups), the size of which is 3 by 3 cells.

## The goal of game

The goal of the medium Sudoku is to fill in the empty cells with missing digits, observing one basic rule – there must be no repetition of the same digit in row, column and sector. However, at the middle level, at the very beginning of the game, the field contains fewer filled cells, which makes it difficult to find the correct position of the missing ones. This is where notes and strategic decisions come into play. You can read more about the interface by following this link.

## Strategies

To solve medium difficulty Sudoku, it is necessary to use the "pencil" notes function. They can be used either to find a solution for a particular cell or to eliminate candidates and remove unnecessary notes from the cell. There are four basic methods of achieving this goal. They are called naked single, hidden single, naked pairs, and hidden pairs. All of these methods require the user to write down each candidate they want to apply to each cell.

### Naked single

If the player finds a cell with a digit that is the only candidate for that place, such a digit is called a naked single. Consequently, the number in question, regardless of the fact that it may be a candidate in other cells of any row, column, or sector, is a solution for that cell.

### Hidden single

Hidden singles follow the same logic, but in the opposite direction. In this case, you may have several candidates for a cell, but only one digit is the solution in that row, column, or sector. It is called "hidden" because other candidates create "noise" (interference, distraction) that makes it difficult to detect.

The following are paired methods that allow the user to exclude only candidates.

### Naked pairs

Naked pairs are two identical pairs of digits that are simultaneously in the same row and column and are candidates for this location. The correct location of each of the digits is not known exactly, but the player knows the exact position of these digits in the cell. Thus, it can be concluded that these candidates can be excluded from other cells of the analyzed row or column.

### Hidden pairs

Hidden pairs are two identical pairs of digits located in opposite corner cells of the 3x3 sector, which cannot be found in other cells. Thus, these two empty cells can be filled only with the first or second pair of digits. They are called this way because they are very difficult to detect on the playing field. Finding them in sectors usually takes a considerable amount of time.

## Puzzle benefits

When you start playing medium Sudoku, you get a number of benefits for yourself:

- Improved logical thinking. When playing the game, a person does not perform any mathematical operations, but they have to, by reasoning logically, put numbers in the right cells, following the existing rules. This contributes to the development of logical thinking person.
- Improved memory. The puzzle promotes the development of logic, which in turn helps to improve memory. The user remembers the rules and the strategies used, and remembers what techniques worked for them. In the same way, the person can remember some important information in other activities.
- Slowing down the negative effects of Alzheimer's disease. Scientists have proven that physical exercise, constant memory training, and maintaining blood pressure at the proper level have an effect on slowing down the disease. An excellent memory training tool is the medium Sudoku puzzles.
- Developing quick thinking. The longer the person plays this puzzle, the faster their brain finds the correct location of any digit. This means that the person's thinking speeds up and they start to think faster. It should also be noted that the game has a timer, which forces the player to perform their actions faster.
- Teaching resourcefulness. The game makes the person show ingenuity, apply non-standard methods of finding the right solution and activate their inner resources.