# Hard Sudoku puzzles

Having played the previous medium level, any player can increase the difficulty and go to this difficult Sudoku, which has an even smaller set of numbers filling the cells on the playing field. In this case, the "pencil" notes function is not a tool to solve hard level Sudoku puzzles, but only acts as an auxiliary element of the interface (for more details about the interface, see the link). To quickly achieve a successful final result, the user must actively engage their logical thinking, wit and patience.

## The goal of game

The goal is to fill in the missing digits (only 1, 2, 3, 4, 5, 6, 7, 8, 9) in the empty cells of the game board, the dimension of which is nine by nine cells. The following basic rule should be taken into account: each of the participating digits should not be repeated in any 1x9 row, 1x9 column or 9x9 sector.

On this site, you can play difficult Sudoku online, without registration, but by registering you can participate in the ratings and compete for first place with other service members.

## Some strategies for solving hard web Sudoku

Print difficult Sudoku. When solving them, you can use different colors. They can mark the numbers that were used. You can also use different symbols to indicate solution options.

Advanced methods used in hard Sudoku are designed to eliminate candidates, help clear the playing field, and calculate the most likely location of a particular digit. The three most commonly used methods at this level are called X-Wing, Swordfish and XY-Wing. They also apply to other more advanced and impossible levels.

### The X-Wing

You can apply the X-Wing strategy when you realize that the same candidate is located in four different grid cells joined by a row and a column and forming a square or rectangle when you draw an imaginary line between them. By mentally connecting the two diagonal ends of this link, the user can determine that only two pairs of numbers can be excluded from this link. If one number is true, the other becomes impossible. The goal is to test these sets and exclude a candidate from any grid cells.

### Swordfish method

When using Swordfish method, you should have three rows containing two cells with the same candidate in each. The arrangement of the cells does not have to be symmetrical, but each must be connected to at least one other column. When combined, these blocks form a closed chain that reveals only two possible sets of their combinations. As with the X-Wing technique, you must then test them both and remove the candidate from the cells that become impossible when both sets are applied.

### The XY-Wing

XY-Wing is applied when you find three cells, each containing only a pair of candidates that share at least one digit between them (e.g., XY/YZ/XZ). Their shape roughly resembles a Y-shape with a cell that works as a stem and two branches. Each branch should separate the candidate from the stem. To simplify the task, draw one line over the stem column and two more over the rows of branches. If the cell where the lines intersect each other contains a number separated by a stem and a branch, you can safely exclude it from the candidates.

## The advantages of playing hard web Sudoku puzzles

When you start solving hard Sudoku puzzles, the game gives you a number of positive benefits:

- Improves your concentration. The user should be focused and should not be distracted by the processes surrounding him when he plays. He completely immerses himself in the game process and is removed from the world around him. Thanks to this, many players learn to concentrate on one thing. Concentration and focus are an important part of many areas of activity, so developing these skills will help you in life.
- Free web difficult Sudoku puzzles give you a sense of accomplishment. Solving the puzzle is a difficult task. Each person considers the solution of any complex task to be an achievement. All these achievements form a person's sense of accomplishment. It motivates a person and sets them up for a positive.
- If you are diagnosed with dementia, mind games and physical exercise will not be able to get rid of it. But research by scientists has shown that constant brain training can minimize the development of dementia. Such training strengthens brain neurons and the connections between them.
- Reduces stress levels and reduces your anxiety. Helps the user regain a sense of balance and tranquility, causing them to forget about everyday problems and activities.
- With this game, the child learns to cope with problems. To solve a Sudoku puzzle of a difficult level (or any other), the child must use logical reasoning and go through a series of trial and error. This turns problem solving into a gameplay.
- It's a great hobby for any person that does not require a lot of investment. Some hobbies are quite expensive. This one is not. This puzzle is printed in many magazines, books and newspapers, which you can purchase at a low price. It's also available on many websites on the subject.
- It gives you an affiliation to a social group and connects you with other people who are passionate about the same activity. Sometimes people get together for dinner with family members or friends. Some people are addicted to online video games with their virtual friends. Others like to go to different events together. And then there are those who want to socialize with other fans of these difficult Sudoku puzzles.