Introduction

Sudoku, also known as Number Place or Nanpure, is a logic-based placement puzzle. The object is to fill the grid so that every column, every row and every 3x3 box contains the digits 1 to 9. The puzzle setter provides a partially completed grid so that there is only one solution.

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History

Number puzzles first appeared in newspapers in the late 19th century, when French puzzle setters began experimenting with removing numbers from magic squares. Le Siècle, a Paris-based daily, published a partially completed 9x9 magic square with 3x3 sub-squares in 1892. It was not a Sudoku because it contained double-digit numbers and required arithmetic rather than logic to solve, but it shared key characteristics: each row, column and sub-square added up to the same number.

Within three years Le Siècle's rival, La France, refined the puzzle so that it was almost a modern Sudoku. It simplified the 9x9 magic square puzzle so that each row and column contained only the numbers 1-9, but did not mark the sub-squares. Although they are unmarked, each 3x3 sub-square does indeed comprise the numbers 1-9. However, the puzzle cannot be considered the first Sudoku because, under modern rules, it has two solutions. The puzzle setter ensured a unique solution by requiring 1-9 to appear in both diagonals.

These weekly puzzles were a feature of newspaper titles including L'Echo de Paris for about a decade but disappeared about the time of the First World War.

According to Will Shortz, the modern Sudoku was most likely designed anonymously by Howard Garns, a 74-year-old retired architect and freelance puzzle constructor, and first published in 1979 by Dell Magazines as Number Place (the earliest known examples of modern Sudoku), because Garns' 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. Sadly, he died in 1989 before getting a chance to see his creation as a worldwide phenomenon.

The puzzle was introduced in Japan by Nikoli in the paper Monthly Nikolist in April 1984 as Suuji wa dokushin ni kagiru, which can be translated as "the numbers must be single" or "the numbers must occur only once." At a later date, the name was abbreviated to Sudoku by Maki Kaji, taking only the first kanji of compound words to form a shorter version. 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.

1997, retired Hong Kong judge Wayne Gould, 59, a New Zealander, saw a partly completed puzzle in a Japanese bookshop. Over six years he developed a computer program to produce puzzles quickly. Knowing that British newspapers have a long history of publishing crosswords and other puzzles, he promoted Sudoku to The Times in Britain, which launched it on 12 November 2004 (calling it Su Doku).

It was rapidly introduced by The Daily Telegraph, the Daily Mail and The Independent. By April and May 2005 the puzzle became a national phenomenon and was introduced to several other national British newspapers including The Guardian, The Sun (where it was labelled Sun Doku), and The Daily Mirror.