What is Sudoku?

Sudoku is a number placement puzzle based on logic rather than mathematics. Sudoku gained worldwide popularity in early 2005 and began selling in the form of puzzle books, handheld electronic versions and board games, as well as appearing in thousands of daily newspapers.

The concept of Sudoku is simple. The puzzle consists of a 9x9 square grid that is divided into nine 3x3 squares, resulting in nine rows and nine columns, for a total of 81 small squares. The unsolved Sudoku puzzle supplies only a few numbers in random squares. To solve the puzzle, the remaining squares must be filled in with the numbers 1 through 9, each appearing only once in each row, column and 3x3 square.

Because Sudoku is logic-based, other puzzles could be created that use the same concept and replace the numbers with other objects, such as colors, letters or shapes. However, Sudoku is aptly named, because the word Sudoku is a Japanese abbreviation loosely meaning “single number”.

In its most basic form, Sudoku comes in the traditional 9x9 square grid with various difficulty levels. The difficulty rating for solving the puzzle is not based on the number of squares with numbers supplied, but rather on their placement on the grid. These supplied numbers are called givens. The complexity involved in solving the puzzles ranges so that anyone can enjoy a Sudoku puzzle that parallels their own ability level. Some variations of the puzzle exist in which the grid is changed to contain more squares or further restrictions are put on the placement of the numbers.

Though this puzzle concept has been around for years under many different names, the modern version was popularized in Japan in 1986, when the puzzle publisher Nikoli discovered a puzzle originally published in Dell Magazines as “Number Place”. Nikoli patented the word Sudoku and began publishing the puzzles in varying difficulty levels, and they became wildly popular in Japan. In 2004, Sudoku's international popularity began when a puzzle was published in a British newspaper as a result of a computer program developed by Wayne Gould that could quickly generate the puzzles. From there, the popularity of the puzzles eventually spread to the United States and elsewhere. The first Sudoku championship was held in March 2006 in Lucca, Italy.