Sudoku

History

Sudoku, also known as "Number Place" in the United States, is a logic-based, combinatorial number-placement puzzle. The objective of the game 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 contain all of the digits from 1 to 9. The puzzle setter provides a partially completed grid, which typically has a unique solution.

The modern Sudoku was most likely designed anonymously by Howard Garns, a 74-year-old retired architect and freelance puzzle constructor from Indiana, and first published in 1979 by Dell Magazines as "Number Place". Garns's name was always present on the list of contributors in issues of Dell Pencil Puzzles and Word Games that included Number Place, and was always absent from issues that did not. He died in 1989 before getting a chance to see his creation as a worldwide phenomenon. Whether or not Garns was familiar with any of the French newspapers listed above is unclear.

The puzzle was introduced in Japan by Nikoli in the paper Monthly Nikolist in April 1984 as Suuji wa dokushin ni kagiru (数字は独身に限る), which also can be translated as "the digits must be single" or "the digits are limited to one occurrence" (In Japanese, dokushin means an "unmarried person"). At a later date, the name was abbreviated to Sudoku (数独) by Maki Kaji (鍜治真起 Kaji Maki), taking only the first kanji of compound words to form a shorter version. "Sudoku" is a registered trademark in Japan and the puzzle is generally referred to as Number Place (ナンバープレース Nanbāpurēsu) or, more informally, a portmanteau of the two words, Num(ber) Pla(ce) (ナンプレ Nanpure). In 1986, Nikoli introduced two innovations: the number of givens was restricted to no more than 32, and puzzles became "symmetrical" (meaning the givens were distributed in rotationally symmetric cells). It is now published in mainstream Japanese periodicals, such as the Asahi Shimbun.

The Times in the United Kingdom began publishing the puzzle on November 12, 2004 after it was introduced to them by Wayne Gould, a Hong Kong judge. It became an international hit in 2005.

Rules

A standard Sudoku puzzle consists of a 9x9 grid, divided into nine 3x3 boxes. Each box contains nine cells, resulting in 81 cells in total. The puzzle is presented with some of the cells already filled in with numbers from 1 to 9. The objective of the puzzle is to fill the rest of the grid with numbers in such a way that each row, column, and 3x3 box contains each of the digits from 1 to 9 exactly once.

Variations

There are many variations of Sudoku. These include but are not limited to:

- Mini Sudoku: A smaller version of the classic Sudoku puzzle, usually 6x6, 4x4, or 2x2. The rules are the same, but the grid and the number range are smaller.

- Alphabetical Sudoku: Instead of numbers, the puzzle uses letters. The rules remain the same.

- Jigsaw Sudoku: Also known as Irregular Sudoku, this version has irregularly shaped groups of squares instead of the traditional 3x3 boxes.

- Killer Sudoku: A combination of Sudoku and Kakuro. This version includes cages, which are groups of cells where the sums of the numbers in the cells are given.

- Hyper Sudoku: Also known as Windoku, this version includes four additional 3x3 regions in the grid.

- Twodoku: This involves two separate puzzles that interact with each other.

Solving Techniques

There are several techniques that can be used to solve Sudoku puzzles. Here are some of the most common ones:

- Elimination: This involves identifying which numbers are already present in a row, column, or box, and then eliminating these numbers as possibilities for other cells in the same row, column, or box.

- Subsets: This technique involves identifying subsets of possible numbers within a row, column, or box. For example, if two cells in a row can only contain the numbers 2 and 3, then these numbers can be eliminated as possibilities for other cells in the same row.

- Crosshatching: This involves looking at a particular box and a particular number, and trying to eliminate that number as a possibility in one or more cells in the box by looking at the numbers present in the intersecting rows and columns.

- Guess and check: This involves making a guess, then following through on the implications of that guess. If the guess leads to a contradiction, then the original guess was incorrect.

Competitions

There are many national and international Sudoku competitions. The World Sudoku Championship is an annual international puzzle competition organised by a member of the World Puzzle Federation. The first championship was held in Lucca, Italy, in 2006. National championships are held in various countries, including the United States, United Kingdom, Germany, and India.

Software

There are many computer programs and online platforms available for generating and solving Sudoku puzzles. Some of these include options for hints, checking answers, and varying levels of difficulty. Some software even allows users to create their own Sudoku puzzles.

In Popular Culture

Sudoku puzzles have become a common feature in many newspapers and magazines. They are also often included in puzzle books and are available as mobile games. The puzzle has been the subject of numerous books and television shows.