Sudoku

Sudoku, called Number Place in some publications, is a type of logic puzzle involving the placement of the digits 1-9 within a 9x9 grid so that each row, column, and 3x3 section of the grid contains each one exactly once. Invented under various names in France in the 1800s, Sudoku puzzles reached the popular market in 1986 when Japanese

Background
The first case of a 9x9 grid that could function as a proper Sudoku was published by the French newspaper La France, under the name ' carré magique diabolique'. The goal, as expressed in the paper, was to fill in the 'magic square' based off the numbers already entered so that no number appeared twice in any row, column, or broken diagonal. While the puzzle presented did not mark off 3x3 regions, the final (unique) solution would still have been a valid Sudoku solution as well, as the usual regions did in fact have each number exactly once. Other French newspapers published similar puzzles from 1895 until around 1914, with no clear reason for why they fell out of popularity.

It wouldn't be until 1979 that the Sudoku would be remade, this time in the US by a man named Howard Garns, who published them anonymously in Dell Magazines under the title 'Number Place'. Despite his version being pretty much identical to what is known today as a Sudoku puzzle, it wasn't until the Japanese publisher Nikoli picked it up that it started to gain popularity.

The Japanese Sudoku was originally called ' dokushin ni kagiru', but was shortened by Maki Kaji to 'Sudoku'. In addition, Nikoli registered the name as a trademark, meaning that while Sudoku is still used for the genre as a whole worldwide, there are still many people and publications that use the generic 'Number Place'.

It wasn't until 1997 that the process to spread Sudoku puzzles outside of Japan began, pioneered by a judge from Hong Kong named Wayne Gould. After seeing a partially-solved puzzle, he dedicated six years to writing a computer program to generate unique puzzles, which he then introduced and sold to The Times in the UK and The Conway Daily Sun in New Hampshire, kicking off the Sudoku craze of the 21st century.

Products of the increased interest in Sudoku puzzles worldwide include the World Sudoku Championship (which began in 2006), multiple game shows, and the popular YouTube channel Cracking The Cryptic.

Puzzle Application
The most basic rules of Sudoku puzzles are that the 9 digits/letters/symbols involved can only occur once in each row/column/3x3square, although some variations exist that introduce more constraints on placement (such as

According to Nikoli, there are only a few rules to creating a Sudoku puzzle, although they aren't strict, and certain publishers may have individual rules that either add to or contradict the ones set by Nikoli.


 * 1) There may be no more than 32 given digits (less than 40% of the grid)
 * 2) The arrangement of numbers must be symmetrical

Both of these rules are reportedly intended to create more enjoyable puzzle, rather than a more difficult/"proper" puzzle. As mentioned, certain publications may put further constraints on the puzzles based on the deductions that need to be made in order to solve it, often to place the puzzle in a particular difficulty range (so that advanced techniques aren't needed to solve a purportedly 'Easy' puzzles).