
History of Sudoku 

Sudoku puzzles are a form of Latin Squares, a concept developed by a Swiss mathematician named Leonhard Euler in the mid 1700's. A Latin Square is an n x n array or matrix filled with n different symbols in which each symbol appears exactly once in each column and row. Howard Garnes, a freelance puzzle maker, came up with the puzzles we now call Sudokus in the late 1970's, and called them Number Place.
The word 'Sudoku' was devised in Japan in the mid 1980's by a puzzle company called Nikoli. 'Su Doku' literally means 'Numbers Single,' or loosely, 'Solitaire with Numbers,' or 'The Numbers Occur only Once.' Nikoli also standardized putting givens in a symmetrical arrangement. For over a decade Sudoku remained primarily in Japan.
In 1997 a man named Wayne Gould came across a Sudoku puzzle in a Japanese bookshop. He was inspired and spent the next few years writing a computer program called Pappocom Sudoku to generate the puzzles in mass. In the Fall of 2004 he convinced the Times to publish his puzzles daily, and within months Sudoku puzzles were showing up in newspapers across England. By the summer of 2005 Sudoku mania had swept across the United States as well, with Sudoku puzzles showing up as commonly as crossword puzzles in newspapers.
In 2006 a collaborative effort on the internet was made to try and discover the world's hardest Sudoku. Hundreds of programmers and Sudoku gurus set out to write their own Sudoku solving programs, and numerous solving methods sprung up. Of these the most notable are Sudoku Explainer, gsf and suexrat. On November 6th, 2006, a Finnish mathematician named Arto Inkala created a puzzle he called AI Etana. AI Etana was accepted by almost all ratings systems as the world's hardest Sudoku puzzle.
AI Etana ushered in a new age of extremely difficult Sudokus. It was discovered that putting givens in diagonal arrangements with respect to the individual boxes would generate puzzles far harder than any yet known up to that point. AI Etana was soon surpassed by immensely difficult Sudokus, the most notable of which are called Easter Monster and Golden Nugget.
A massive effort also went out to see how few givens can still give a unique solution to a Sudoku. It was determined and generally accepted that this minimum number is 17, since after years of search nobody has yet been able to produce a Sudoku with 16 or less givens that has a unique solution. Here is one example of a Sudoku with 17 givens. If the traditional alignment of boxes is done away with, the number of givens can go down significantly. The minimum theoretical number of givens is 8, since if there are two different values not represented, they can be interchanged and thus create two possible solutions. Here is an example of the definitive record of a nontraditional alignment with 8 givens.






