Sudoku is a logic-based number-placement puzzle. The goal is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 subgrids that compose the grid (also called “boxes”, “blocks”, or “regions”) contains all of the digits from 1 to 9. The puzzle setter provides a partially completed grid, which for a well-posed puzzle has a unique solution.
**History of Sudoku**
While precursors to Sudoku appeared as early as 1895 in French newspapers, the modern game of Sudoku was invented in 1979 in Indianapolis. It gained widespread popularity in 1986 when the Japanese puzzle publisher Nikoli discovered and published it.
**How to Play Sudoku**
The game uses a grid of nine squares by nine squares, subdivided into nine 3×3 regions. The objective is to place the digits 1 through 9 into the empty squares, ensuring that each digit appears only once in each row, column, and 3×3 region. Some squares are pre-filled with numbers, known as “givens” or “clues,” which serve as starting points.
**Difficulty Levels**
Despite its simple construction, Sudoku can be challenging and require significant mental effort. Puzzle difficulty is often ranked by publishers, typically using a scale of 4 to 5 levels to categorize puzzles based on complexity.
**Accessibility**
Sudoku puzzles are widely available in newspapers, magazines, and dedicated puzzle books. They can also be played as computer games or accessed for free on websites, many of which offer the ability to generate custom puzzles.