Sudoku - The Game
Quick Start
Sudoku is a logic game based in a 9x9 grid divided in rows, columns and 3x3 regions. The game starts with a partially completed grid and the objective is to complete it so that each row, column and 3x3 box contains all numbers from 1 to 9.
Here you can see an example of a Sudoku game ready to play and below the game completed.
Observe in the solution that in each row, column or 3x3 box all numbers from 1 to 9 are placed once and only once.
A good Sudoku game should have only one posible solution and can be symmetric or not.
A Sudoku game is symmetric if the initial numbers are placed in a symmetrical pattern, with a 180 degree rotation the pattern looks the same. The Sudoku example is symmetric.
With the FreeSudoku game you can generate symmetric and non-symmetric games. I don't know if there is any difference between symmetric and normal Sudokus in difficulty. I supose that it is an aesthetical question that comes from the time of the first Sudoku publications. Most of the crosswords games in the newspapers are also symmetric.
This example was generated with the FreeSudoku program, selecting the lowest level of difficulty. You can select between 4 levels and when the game is generated you can check the estimated difficulty degree (from 1 to about 300) for that game, under Help - About.
For this game the difficulty degree was '3'. In a medium game you can get a degree of about '25' and in hard game generated with FreeSudoku it can be '150', '200' or more, depending on how many hard strategies you have to use to solve it.
A bit of history
Is posible that the first games were created based in the work of Leonhard Euler in the 18th century. Euler didn't create the game, but introduced the 'Latin Square' to do some probabilistics calculations.In the late 19th century the French newspapers 'Le Siècle' and 'La France' published puzzles similar to Sudoku, in 1892 and during about a decade.
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 (the earliest known examples of modern Sudoku). 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 (数字は独身に限る, Suuji wa dokushin ni kagiru?), which can be translated as "the digits must be single" or "the digits are limited to one occurrence".
At a later date, the name was abbreviated to Sudoku by Maki Kaji (鍜治 真起, Kaji Maki?), 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". It is now published in mainstream Japanese periodicals, such as the Asahi Shimbun.
A worldwide phenomenon
In 1997, the retired Hong Kong judge Wayne Gould (New Zealander) saw a partly completed puzzle in a Japanese bookshop and over six years developed a computer program to produce puzzles quickly (like FreeSudoku). He promoted Sudoku to 'The Times' in Britain, which launched it on 12 November 2004, calling it Su Doku.The rapid rise of Sudoku in Britain from relative obscurity to a front-page feature in national newspapers attracted commentary in the media and parody, such as when The Guardian's G2 section advertised itself as the first newspaper supplement with a Sudoku grid on every page.
In the United States, the first newspaper to publish a Sudoku puzzle by Wayne Gould was The Conway Daily Sun (New Hampshire), in 2004.
Sudoku software is now also very popular on PCs, websites, and mobile phones. It has also been released on portable video game handhelds such as the Nintendo DS, PlayStation Portable, and the Game Boy Advance.
Today Sudoku is one of the most popular 'paper' and computer games and is played by millions of people worldwide.