Sudoku Laws

[Graciano Goudreau]

Mostsudoku puzzles come with a few of the boxes already filled in, so you can use those freebie clues as a jumping off point for solving and work backwards. The fewer numbers already filled in the more difficult it will be.

Outside of that, there is no straightforward "how to play" sudoku guide. The only hard and fast rule is not to repeat numbers. Suduku.com advises using the process of elimination, or deductive reasoning.

This puzzle, like any game of logic, is a workout for your brain. Healthline reported in May of 2019 on a cross-sectional study showing participants who engaged in games like sudoku and crosswords performed better on subsequent tests.

The study went so far as to say those who do puzzles like sudoku have brain function that is equal to 10 years younger than their actual age. More research is needed to definitively prove this conclusion, study authors clarify, but in the meantime, not a bad idea to keep up with your puzzling to sharpen cognitive skills!

A brief history, as provided by the Cornell University mathematics department. American Howard Garns in 1979 invented sudoku as we know it, and published it originally as a puzzle in Dell Magazines with the name "Numbers in Place."

When people over 50 engage in thought games like sudoku and crossword puzzles, their brains function better, according to a study in the International Journal of Geriatric Psychiatry. In fact, study participants who worked such puzzles more than once a day had superior cognitive performance in key areas, such as reasoning, attention and memory.

Many puzzles will leave one or two blanks either in a line or in a box. A line might be missing a 5 and a 6, but a box along that line will already have a 6 in it, so you know this blank must be a 5, and the other blank must be the 6. The same may be the case for one or two missing numbers in the smaller boxes. Filling these blanks will get you on your way to a solution.

As you fill in the easy solutions, you may start to find other missing numbers that are easy to place. In the above example, the box now has a 5, and that may help you solve that 33 area, or might help you solve the lines that cross that area.

Remember that although you want to finish a puzzle, the point is to enjoy the challenge and work your brain as you relax. If you find yourself getting frustrated, walk away. Let your mind clear and try again later. The most important thing is to have fun.

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I'm working on a javascript sudoku, and as far as validation of input goes, I'm stumped. As each value is entered into the sudoku table, I have an onkeyup triggering a function which I am attempting to use to make sure that no value enters a row/column/box where such a value already exists. This is my first time attempting such a project, so I apologize in advance for the noob code.

I know that using x as a placeholder is probably not the best plan, but at this point it is mostly for testing purposes so values being input wont exist before the testing starts. Where I attempt to check row, I'm obviously trying to loop through the array at indexes (0,0) -> (0,8) and check that no value exists twice in that row. I had this working to check a single row, but seem to have broken it while attempting to add more rows to check.

French newspapers featured variations of the Sudoku puzzles in the 19th century, and the puzzle has appeared since 1979 in puzzle books under the name Number Place.[5] However, the modern Sudoku only began to gain widespread popularity in 1986 when it was published by the Japanese puzzle company Nikoli under the name Sudoku, meaning "single number".[6] It first appeared in a U.S. newspaper, and then The Times (London), in 2004, thanks to the efforts of Wayne Gould, who devised a computer program to rapidly produce unique puzzles.

Number puzzles appeared in newspapers in the late 19th century, when French puzzle setters began experimenting with removing numbers from magic squares. Le Sicle, a Paris daily, published a partially completed 99 magic square with 33 subsquares on November 19, 1892.[7] 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 subsquare added up to the same number.

The modern Sudoku was most likely designed anonymously by Howard Garns, a 74-year-old retired architect and freelance puzzle constructor from Connersville, Indiana, and first published in 1979 by Dell Magazines as Number Place (the earliest known examples of modern Sudoku).[1] 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.[10] He died in 1989 before getting a chance to see his creation as a worldwide phenomenon.[10] Whether or not Garns was familiar with any of the French newspapers listed above is unclear.

In 1997, Hong Kong judge Wayne Gould saw a partly completed puzzle in a Japanese bookshop. Over six years, he developed a computer program to produce unique puzzles rapidly.[5] 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 November 12, 2004 (calling it Su Doku). The first letter to The Times regarding Su Doku was published the following day on November 13 from Ian Payn of Brentford, complaining that the puzzle had caused him to miss his stop on the tube.[12] Sudoku puzzles rapidly spread to other newspapers as a regular feature.[5][13]

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).[14] Recognizing the different psychological appeals of easy and difficult puzzles, The Times introduced both, side by side, on June 20, 2005. From July 2005, Channel 4 included a daily Sudoku game in their teletext service. On August 2, the BBC's program guide Radio Times featured a weekly Super Sudoku with a 1616 grid.

The world's first live TV Sudoku show, Sudoku Live, was a puzzle contest first broadcast on July 1, 2005, on Sky One. It was presented by Carol Vorderman. Nine teams of nine players (with one celebrity in each team) representing geographical regions competed to solve a puzzle. Each player had a hand-held device for entering numbers corresponding to answers for four cells. Phil Kollin of Winchelsea, England, was the series grand prize winner, taking home over 23,000 over a series of games. The audience at home was in a separate interactive competition, which was won by Hannah Withey of Cheshire.

Later in 2005, the BBC launched SUDO-Q, a game show that combined Sudoku with general knowledge. However, it used only 44 and 66 puzzles. Four seasons were produced before the show ended in 2007.

In 2006, a Sudoku website published songwriter Peter Levy's Sudoku tribute song,[16] but quickly had to take down the MP3 file due to heavy traffic. The Japanese Embassy also nominated the song for an award, with Levy doing talks with Sony in Japan to release the song as a single.[17]

Sudoku software is very popular on PCs, websites, and mobile phones. It comes with many distributions of Linux. The software has also been released on video game consoles, such as the Nintendo DS, PlayStation Portable, the Game Boy Advance, Xbox Live Arcade, the Nook e-book reader, Kindle Fire tablet, several iPod models, and the iPhone. Many Nokia phones also had Sudoku. In fact, just two weeks after Apple Inc. debuted the online App Store within its iTunes Store on July 11, 2008, nearly 30 different Sudoku games were already in it, created by various software developers, specifically for the iPhone and iPod Touch. One of the most popular video games featuring Sudoku is Brain Age: Train Your Brain in Minutes a Day!. Critically and commercially well-received, it generated particular praise for its Sudoku implementation[18][19][20] and sold more than 8 million copies worldwide.[21] Due to its popularity, Nintendo made a second Brain Age game titled Brain Age2, which has over 100 new Sudoku puzzles and other activities.

In June 2008, an Australian drugs-related jury trial costing over A$ 1 million was aborted when it was discovered that four or five of the twelve jurors had been playing Sudoku instead of listening to the evidence.[22]

Under the name "Mini Sudoku", a 66 variant with 32 regions appears in the American newspaper USA Today and elsewhere. The object is the same as that of standard Sudoku, but the puzzle only uses the numbers 1 through 6. A similar form, for younger solvers of puzzles, called "The Junior Sudoku", has appeared in some newspapers, such as some editions of The Daily Mail.

Another common variant is to add limits on the placement of numbers beyond the usual row, column, and box requirements. Often, the limit takes the form of an extra "dimension"; the most common is to require the numbers in the main diagonals of the grid to also be unique. The aforementioned "Number Place Challenger" puzzles are all of this variant, as are the Sudoku X puzzles in The Daily Mail, which use 66 grids.

The killer sudoku variant combines elements of sudoku and kakuro. A killer sudoku puzzle is made up of 'cages', typically depicted by boxes outlined with dashes or colours. The sum of the numbers in a cage is written in the top left corner of the cage, and numbers cannot be repeated in a cage.

Puzzles constructed from more than two grids are also common. Five 99 grids that overlap at the corner regions in the shape of a quincunx is known in Japan as Gattai 5 (five merged) Sudoku. In The Times, The Age, and The Sydney Morning Herald, this form of puzzle is known as Samurai Sudoku. The Baltimore Sun and the Toronto Star publish a puzzle of this variant (titled High Five) in their Sunday edition. Often, no givens are placed in the overlapping regions. Sequential grids, as opposed to overlapping, are also published, with values in specific locations in grids needing to be transferred to others.

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