Sudoku

What is Sudoku?
Sudoku is a puzzle game typically played on a 9x9 square grid. This grid is divided into nine 3x3 sub-squares (called regions or boxes). The goal of the game is to place the numbers 1 to 9 in the empty cells of the grid, but this placement is governed by specific rules. Sudoku does not require mathematical calculations; only logical thinking and careful analysis are required. The game is available in different difficulty levels: easy, medium, hard, and expert.

Rules of Sudoku
The basic rules of Sudoku are simple and clear:

Each row must contain the numbers 1 to 9: Each row of the 9x9 grid must contain the numbers 1 to 9 exactly once. The same number cannot appear more than once in a row.
Each column must contain the numbers 1 to 9: Just like the rows, each column must contain the numbers 1 to 9 only once.
Each 3x3 area must contain the numbers 1 to 9: The grid is divided into nine 3x3 sub-areas. Each 3x3 area must contain the numbers 1 to 9 once.
Starting numbers are fixed: At the beginning of the game, numbers (clues) are provided in some cells of the grid. These numbers cannot be changed and form the basis for the solution.
How to Play Sudoku?
Starting: The player begins with a partially filled 9x9 grid. The number of numbers provided depends on the difficulty level of the puzzle (easy puzzles have more clues, difficult puzzles have fewer clues).
Filling in the Empty Cells: The player places numbers from 1 to 9 in the empty cells. Each placement must follow the rules for the row, column, and 3x3 area.
Using Logic: The player uses logical deduction to determine which number can be placed in which cell. For example, if a row contains numbers 1 through 8, the missing 9 must be placed in one of the empty cells in that row.
Error Checking: If the player places a number incorrectly, solving the puzzle can become impossible. Therefore, careful analysis and sometimes trial and error are required.
Completion: The puzzle is solved when all cells are filled with the correct numbers.
Sudoku Strategies
Some basic and advanced strategies used to solve Sudoku are:

Naked Singles: When only one number fits a cell, that number is placed directly. For example, if only 5 is possible for a cell, 5 is written in that cell.
Hidden Singles: When a number can only be placed in one cell in a row, column, or region, that number is written in that cell.
Pairs and Triples: If two cells in a row, column, or region can only contain the same two numbers, those numbers are subtracted from the other cells.
Locked Candidates: When a number can only appear in a specific row or column within a region, that number is removed from the other regions.
X-Wing and Swordfish: These are more advanced techniques. They are used to eliminate possibilities by using the symmetrical patterns formed by numbers across rows and columns.
Trial-and-Error: In challenging puzzles, when more than one number appears suitable for a cell, choose one number and continue. If this is incorrect, go back and try another possibility.