A sudoku puzzle...

...and its solution numbers marked in red

Sudoku (数独, sūdoku^?) listen (help· info) is a logic-based number placement puzzle. The objective is to fill a 9×9 grid so that each column, each row, and each of the nine 3×3 boxes (also called blocks or regions) contains the digits from 1 to 9, only one time each (that is, exclusively). The puzzle setter provides a partially completed grid. Sodoku is a bacterial zoonotic disease. ... Image File history File links Sudoku-by-L2G-20050714. ... Image File history File links Sudoku-by-L2G-20050714. ... Image File history File links Sudoku-by-L2G-20050714_solution. ... Image File history File links Sudoku-by-L2G-20050714_solution. ... Image File history File links Sudoku. ... Logic (from Classical Greek λόγος logos; meaning word, thought, idea, argument, account, reason, or principle) is the study of the principles and criteria of valid inference and demonstration. ... A puzzle undone, which forms a cube Puzzle cube; a type of puzzle For other uses, see Puzzle (disambiguation). ...

Completed Sudoku puzzles are a type of Latin square, with an additional constraint on the contents of individual regions. Leonhard Euler is sometimes incorrectly cited as the source of the puzzle, based on his work with Latin squares.^[1] A Latin square is an n × n table filled with n different symbols in such a way that each symbol occurs exactly once in each row and exactly once in each column. ... Leonhard Paul Euler (pronounced Oiler; IPA ) (April 15, 1707 – September 18 [O.S. September 7] 1783) was a pioneering Swiss mathematician and physicist, who spent most of his life in Russia and Germany. ...

The modern puzzle was invented by an American architect, Howard Garns, in 1979 and published by Dell Magazines under the name "Number Place".^[2] It became popular in Japan in 1986, after it was published by Nikoli and given the name Sudoku, meaning single number. ^[3] It became an international hit in 2005. Sudoku )   is a logic-based placement puzzle. ... Also: 1979 by Smashing Pumpkins. ... Dell Magazines is a company founded by George T. Delacorte Jr. ... Year 1986 (MCMLXXXVI) was a common year starting on Wednesday (link displays 1986 Gregorian calendar). ... Nikoli (ニコリ) is a Japanese publisher that specializes in games and, especially, logic puzzles. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ...

Introduction

The name Sudoku means "single digits"^{[4][5][6][7][8][9]}. The name is a trademark of puzzle publisher Nikoli Co. Ltd. in Japan^[10]. The word sudoku derives from the Japanese phrase "Sūji wa dokushin ni kagiru," meaning "the numbers must be single," or "the numbers must occur only once." In Japanese, the word is pronounced IPA: [sɯːdokɯ]; in English, it is usually IPA: /səˈdoʊkuː/. Other Japanese publishers refer to the puzzle as Number Place, the original U.S. title, or as "Nanpure" for short.^[11] Some publishers spell the title as "Su Doku". The numerals in Sudoku puzzles are used for convenience; arithmetic relationships between numerals are irrelevant. Any set of distinct symbols will do; letters, shapes, or colours may be used without altering the rules. In fact, ESPN published Sudoku puzzles substituting the positions on a baseball field for the numbers 1 through 9; and Viz magazine published a Doctor Who version of the game, using images of the television series' first nine leading actors in place of the numerals. Dell Magazines, the puzzle's originator, has been using numerals for Number Place in its magazines since they first published it in 1979^[11]. <33 “(TM)” redirects here. ... Nikoli (ニコリ) is a Japanese publisher that specializes in games and, especially, logic puzzles. ... The English language is a West Germanic language that originates in England. ... ESPN, formerly an acronym for Entertainment and Sports Programming Network, is an American cable television network dedicated to broadcasting and producing sports-related programming 24 hours a day. ... Viz is a method of introducing a list or a series. ... This article is about the television series. ... Dell Magazines is a company founded by George T. Delacorte Jr. ...

Strategies

The strategy for solving a puzzle may be regarded as comprising a combination of three processes: scanning, marking up, and analyzing. The approach to analysis may vary according to the concepts and the representations on which it is based.

The top right region must contain a 5. By hatching across and up from 5s elsewhere, the solver can eliminate all the empty cells in the region which cannot contain a 5. This leaves only one possibility (shaded green).

Image File history File links Cross-hatching. ... Image File history File links Cross-hatching. ...

Doubles and triples

Finding pairs or doubles can be helpful in finding a solution. If a pair is found in a row where those 2 squares aren't the only open squares, those numbers can be cancelled out of that row. The same goes for triples.

Scanning

Scanning is performed at the outset and throughout the solution. Scans need be performed only once between analyses. Scanning consists of two techniques:

• Cross-hatching: The scanning of rows to identify which line in a region may contain a certain numeral by a process of elimination. The process is repeated with the columns. It is important to perform this process systematically, checking all of the digits 1–9.
• Counting 1–9 in regions, rows, and columns to identify missing numerals. Counting based upon the last numeral discovered may speed up the search. It also can be the case, particularly in tougher puzzles, that the best way to ascertain the value of a cell is to count in reverse—that is, by scanning the cell's region, row, and column for values it cannot be, in order to see what remains.

Advanced solvers look for "contingencies" while scanning, narrowing a numeral's location within a row, column, or region to two or three cells. When those cells lie within the same row and region, they can be used for elimination during cross-hatching and counting. Puzzles solved by scanning alone without requiring the detection of contingencies are classified as "easy"; more difficult puzzles are not readily solved by basic scanning alone.

Logically, every sudoku puzzle, regardless of difficulty, is solved via scanning heuristics. In a true sudoku puzzle, every number has a necessary position in each part of the grid which can be deduced from the description or if you prefer definition of what a "true" sudoku is. The only difference between solving advanced puzzles and simpler puzzles is not the techniques used to solve the puzzle but recognizing the logical implications of the scanning heuristic. One such implication would be recognizing logical "contingencies" which just basically means narrowing down the possibilities of a given square via the relations between every other square.

A method for marking likely numerals in a single cell by the placing of pencil dots. To reduce the number of dots used in each cell, the marking would only be done after as many numbers as possible have been added to the puzzle by scanning. Dots are erased as their corresponding numerals are eliminated as candidates.

The partially filled sub-square determines that 3,5, and 6 must go in the top row. These create a contingency for the far right hatched cell based on the complete row across. It must be a 4.

Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ...

Marking up

Scanning stops when no further numerals can be discovered, making it necessary to engage in logical analysis. One method to guide the analysis is to mark candidate numerals in the blank cells.

Subscript notation

In subscript notation, the candidate numerals are written in subscript in the cells. Because puzzles printed in a newspaper are too small to accommodate more than a few subscript digits of normal handwriting, solvers may create a larger copy of the puzzle. Using two colours, or mixing pencil and pen marks can be helpful.

Dot notation

The dot notation uses a pattern of dots in each square, where the dot position indicates a number from 1 to 9. The dot notation can be used on the original puzzle. Dexterity is required in placing the dots, since misplaced dots or inadvertent marks inevitably lead to confusion and may not be easily erased.

An alternative technique is to mark the numerals that a cell cannot be. The cell starts empty and as more constraints become known, it slowly fills until only one mark is missing. Assuming no mistakes are made and the marks can be overwritten with the value of a cell, there is no longer a need for any erasures.

(click to see larger version) An analysis in Sudoku, done in superscript notation, with all possible values for the squares written in. There are three squares which contain only three values: 4, 6, and 8. If 4, 6, or 8 were written in any square where they're red, it would be impossible to complete the squares where they're blue. Therefore, the numbers in red can be erased. This logic works with rows, columns, sections, and diagonals. (if applicable)

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Analysis

The two main approaches to analysis are "candidate elimination"^[12] and "what-if".^[13] In "candidate elimination", progress is made by successively eliminating candidate numerals from cells to leave one choice. After each answer has been achieved, another scan may be performed—usually checking to see the effect of the contingencies. In general, if entering a particular numeral prevents completion of the other necessary placements, then the numeral in question can be eliminated as a candidate. One method works by identifying "matched cell groups". For instance, if precisely two cells within a scope (a particular row, column, or region) contain the same two candidate numerals (p,q), or if precisely three cells within a scope contain the same three candidate numerals (p,q,r), these cells are said to be matched. The placement of those candidate numerals anywhere else within that same scope would make a solution impossible; therefore, those candidate numerals can be deleted from all other cells in the scope.

In the "what-if" approach (also called "guess-and-check", "bifurcation", "backtracking" and "Ariadne's thread"), a cell with two candidate numerals is selected, and a guess is made. The steps are repeated until a duplication is found or a cell is left without a possible candidate, in which case the alternative candidate must be the solution. For each cell's candidate, the question is posed: 'will entering a particular numeral prevent completion of the other placements of that numeral?' If the answer is 'yes', then that candidate can be eliminated. If the "what-if" exercises for both candidates show that either one is possible, another pair should be tried. Alternatively, if the "what-if" exercises for both candidates imply an identical result, then that result must be true. The what-if approach requires a pencil and eraser or a good layout memory. Backtracking is a type of algorithm that is a refinement of brute force search. ... Ariadnes thread, named for the legend of Ariadne, is the term used to describe the solving of a problem with multiple apparent means of proceeding - such as a physical maze, a logic puzzle, or an ethical dilemma - through an exhaustive application of logic to all available routes. ...

There are three kind of conflicts, which can appear during puzzle solving:

1. basic conflicts - there are only N-1 different candidates in N cell in the area
2. fish conflicts - when eliminating number from N rows/columns, it will disappear also from N+1 columns/rows.
3. unique conflicts - this pattern means multiple solutions, all numbers in the pattern exist exactly two times in every area, row and column. If there is only one candidate in the cell, any virtual candidate can be added.

Encountering any of those would indicate that the puzzle is not uniquely solvable. Encountering any of them as a consequence of "what-if" indicates that an untried alternative is correct.

Computer solutions

There are three general approaches taken in the creation of serious Sudoku-solving programs: human solving methods, rapid-style methods, and pure brute-force algorithms. Human-style solvers will typically operate by maintaining a mark-up matrix, and search for contingencies, matched cells, and other elements that a human solver can utilize in order to determine and exclude cell values.

Many rapid-style solvers employ backtracking searches, with various pruning techniques also being used in order to help reduce the size of the search tree. The term rapid-style may be misleading: Most human-style solvers run considerably faster than a rapid-style solver, although the latter takes less time to write and is more easily adapted to larger grids. A purely brute-force algorithm is very simple and finds a solution to a puzzle essentially by "counting" upward until a string of eighty-one digits is constructed which satisfies the row, column, and box constraints of the puzzle. Backtracking is a type of algorithm that is a refinement of brute force search. ...

Rapid solvers are preferred for trial-and-error puzzle-creation algorithms, which allow for testing large numbers of partial problems for validity in a short time; human-style solvers can be employed by hand-crafting puzzlesmiths for their ability to rate the challenge of a created puzzle and show the actual solving process their target audience can be expected to follow.

Although typical Sudoku puzzles (with 9×9 grid and 3×3 regions) can be solved quickly by computer, the generalization to larger grids is known to be NP-complete. Various optimisation methods have been proposed for large grids. In complexity theory, the NP-complete problems are the most difficult problems in NP, in the sense that they are the ones most likely not to be in P. The reason is that if you could find a way to solve an NP-complete problem quickly, then you could use...

Details of computer solutions may be found on the page on the Algorithmics of Sudoku. It has been suggested that this article or section be merged into Mathematics of Sudoku. ...

Difficulty ratings

The difficulty of a puzzle is based on the relevance and the positioning of the given numbers rather than their quantity. Surprisingly, most of the time the number of givens does not reflect a puzzle's difficulty. Computer solvers can estimate the difficulty for a human to find the solution, based on the complexity of the solving techniques required. Some online versions offer several difficulty levels.

Most publications sort their Sudoku puzzles into four or five rating levels, although the actual cut-off points and the names of the levels themselves can vary widely. Typically, however, the titles are synonyms of "easy", "intermediate", "hard", and "challenging" (also known as "diabolical" or "evil"). An easy puzzle can be solved using only scanning; an intermediate puzzle may take markup to solve; a hard or challenging puzzle will usually take analysis.

Another approach is to rely on the experience of a group of human test solvers. Puzzles can be published with a median solving time rather than an algorithmically defined difficulty level.

Difficulty is a very complex topic, subject to much debate on the Sudoku forums, because it may depend on the concepts and visual representations one is ready to use.

Construction

Building a Sudoku puzzle can be performed by predetermining the locations of the givens and assigning them values only as needed to make deductive progress. This technique gives the constructor greater control over the flow of puzzle solving, leading the solver along the same path the compiler used in building the puzzle. Great caution is required, however, as failing to recognize where a number can be logically deduced at any point in construction—regardless of how tortuous that logic may be—can result in an unsolvable puzzle when defining a future given contradicts what has already been built. Building a Sudoku with symmetrical givens is a simple matter of placing the undefined givens in a symmetrical pattern to begin with.

Nikoli Sudoku are hand-constructed, with the author being credited; the givens are always found in a symmetrical pattern.^[14] Dell Number Place Challenger (see Variants below) puzzles also list authors. The Sudoku puzzles printed in most UK newspapers are apparently computer-generated but employ symmetrical givens; The Guardian famously claimed that because they were hand-constructed, their puzzles would contain "imperceptible witticisms" that would be very unlikely in computer-generated Sudoku. Nikoli (ニコリ) is a Japanese publisher that specializes in games and, especially, logic puzzles. ... Wit is a form of intellectual humour, based on manipulation of concepts; a wit is someone who excels in witty remarks, typically in conversation and spontaneously, since wit carries the connotation of speed of thought. ...

Variants

A nonomino Sudoku puzzle, sometimes also known as a Jigsaw Sudoku, for instance in the Sunday Telegraph

Solution numbers in red for above puzzle

Even though the 9×9 grid with 3×3 regions is by far the most common, variations abound: sample puzzles can be 4×4 grids with 2×2 regions; 5×5 grids with pentomino regions have been published under the name Logi-5; the World Puzzle Championship has previously featured a 6×6 grid with 2×3 regions and a 7×7 grid with six heptomino regions and a disjoint region. Larger grids are also possible. The Times offers a 12×12-grid Dodeka sudoku with 12 regions of 4×3 squares each. Dell regularly publishes 16×16 Number Place Challenger puzzles (the 16×16 variant often uses 1 through G rather than the 0 through F used in hexadecimal). Nikoli offers 25×25 Sudoku the Giant behemoths. Image File history File links Nonomino_Sudoku. ... Image File history File links Nonomino_Sudoku. ... For the Rolling Stones song, see Jigsaw Puzzle A jigsaw puzzle is a tiling puzzle that requires the assembly of numerous small, often oddly shaped, interlocking and tessellating pieces. ... This article deals with The Daily Telegraph in Britain, see The Daily Telegraph (Australia) for the Australian publication The Daily Telegraph is a British broadsheet newspaper founded in 1855. ... Image File history File links Nonomino_Sudoku_solution. ... Image File history File links Nonomino_Sudoku_solution. ... A pentomino is a polyomino composed of five (Greek πέντε / pente) congruent squares, connected orthogonally. ... The World Puzzle Championship is an annual international puzzle competition run by the World Puzzle Federation. ... ... In mathematics and computer science, hexadecimal, base-16, or simply hex, is a numeral system with a radix, or base, of 16, usually written using the symbols 0–9 and A–F, or a–f. ...

Another common variant is for additional restrictions to be enforced on the placement of numbers beyond the usual row, column, and region requirements. Often the restriction takes the form of an extra "dimension"; the most common is for the numbers in the main diagonals of the grid to also be required to 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 6×6 grids. The Daily Mail is a British newspaper and the oldest tabloid, first published in 1896. ...

Another variant is the genuine combination of Sudoku with Kakuro on a 9 x 9 grid, called Cross Sums Sudoku, in which clues are given in terms of cross sums. The clues can also be given by cryptic alphametics in which each letter represents a single digit from 0 to 9. An excellent example is NUMBER+NUMBER=KAKURO which has a unique solution 186925+186925=373850. Another example is SUDOKU=IS*FUNNY whose solution is 426972=34*12558.

Hypersudoku puzzle.

Solution to Hypersudoku puzzle.

Many newspapers include the popular Hypersudoku. The layout is identical to a normal Sudoku, but with additional interior areas defined in which the numbers 1 to 9 must appear. The solving algorithm is slightly different from the normal Sudoku puzzles because of the leverage on the overlapping squares. This overlap gives you more information to logically reduce the possibilities in the remaining squares. The approach to playing is still similar to sudoku but with possibly more emphasis on scanning the squares and overlap rather than columns and rows. Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... // Also known as hyper-sudoku or hyper sudoku is another variant of sudoku. ... Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... // Also known as hyper-sudoku or hyper sudoku is another variant of sudoku. ...

Puzzles constructed from multiple Sudoku grids are common. Five 9×9 grids which 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. Puzzles with twenty or more overlapping grids are not uncommon in some Japanese publications. Often, no givens are to be found in overlapping regions. Sequential grids, as opposed to overlapping, are also published, with values in specific locations in grids needing to be transferred to others. Five dots forming a quincunx A quincunx is the arrangement of five units in the pattern corresponding to the five-spot on dice, playing cards, or dominoes. ... The Times is a national newspaper published daily in the United Kingdom (and the Kingdom of Great Britain before the United Kingdom existed) since 1788 when it was known as The Daily Universal Register. ... This article does not cite any references or sources. ... This article or section does not cite its references or sources. ...

Alphabetical variations have also emerged; there is no functional difference in the puzzle unless the letters spell something. Some variants, such as in the TV Guide, include a word reading along a main diagonal, row, or column once solved; determining the word in advance can be viewed as a solving aid. The Code Doku^[15] devised by Steve Schaefer has an entire sentence embedded into the puzzle; the Super Wordoku^[16] from Top Notch embeds two 9-letter words, one on each diagonal. It is debatable whether these are true Sudoku puzzles: although they purportedly have a single linguistically valid solution, they cannot necessarily be solved entirely by logic, requiring the solver to determine the embedded words. Top Notch claims this as a feature designed to defeat solving programs. Cludoku is an alphabetical variation that is solved only by logic, after which the solver then has to find solutions to crossword-style clues found in the completed grid. TV Guide is the name of two North American weekly magazines about television programming, one in the United States and one in Canada. ... Cludoku (also called Cluedoku) is essentially Sudoku employing letters instead of the traditional numbers 1-9 plus: a) Clues, similar to those found in crosswords, and b) Word Search – not only the traditional straight-line search but also Boggle-like zig-zag searching. ...

There is also a Sudoku version of the Rubik's Cube named Sudokube. Variations of Rubiks Cubes (from left to right: Rubiks Revenge, Rubiks Cube, Professors Cube, & Pocket Cube). ... A scrambled sudokube puzzle Sudokube is a variation on a Rubiks Cube in which each face resembles one-ninth of a Sudoku grid: the numbers from one to nine. ...

Finally, some of the more notable single-instance variations are:

• A three-dimensional Sudoku puzzle was invented by Dion Church and published in the Daily Telegraph in May 2005.
• The 2005 U.S. Puzzle Championship includes a variant called Digital Number Place: rather than givens, most cells contain a partial given—a segment of a number, with the numbers drawn as if part of a seven-segment display.
• The Sudoku_Solitaire concept was created by Leonard C. Russell for bluenitesystems. In it the numbers needed to complete the puzzle are played from a deck and discard pile, just like in the Solitaire card game.

This article deals with The Daily Telegraph in Britain, see The Daily Telegraph (Australia) for the Australian publication The Daily Telegraph is a British broadsheet newspaper founded in 1855. ... A seven-segment display (abbreviation: 7-seg(ment) display), less commonly known as a seven-segment indicator, is a form of display device that is an alternative to the more complex dot-matrix displays. ...

Mathematics of Sudoku

Main article: Mathematics of Sudoku

Leonhard Euler's famous thirty-six officers' puzzle

A completed Sudoku grid is a special type of Latin square with the additional property of no repeated values in any 3×3 block. The relationship between the two theories is now completely known, after Denis Berthier has proven in his recent book, "The Hidden Logic of Sudoku"^[17], that a first order formula that does not mention blocks (also called boxes or regions) is valid for Sudoku if and only if it is valid for Latin Squares. The class of Sudoku puzzles consists of a partially completed row-column grid of cells partitioned into N regions each of size N cells, to be filled in using a prescribed set of N distinct symbols (typically the numbers {1, ..., N}), so that each row, column and region contains exactly... Image File history File links Euler_36. ... Image File history File links Euler_36. ... Leonhard Paul Euler (pronounced Oiler; IPA ) (April 15, 1707 – September 18 [O.S. September 7] 1783) was a pioneering Swiss mathematician and physicist, who spent most of his life in Russia and Germany. ... A Latin square is an n × n table filled with n different symbols in such a way that each symbol occurs exactly once in each row and exactly once in each column. ...

The number of classic 9×9 Sudoku solution grids was shown in 2005 by Bertram Felgenhauer and Frazer Jarvis to be 6,670,903,752,021,072,936,960^[18] (sequence A107739 in OEIS) : this is roughly 0.00012% the number of 9×9 Latin squares. Various other grid sizes have also been enumerated—see the main article for details. The number of essentially different solutions, when symmetries such as rotation, reflection and relabelling are taken into account, was shown by Ed Russell and Frazer Jarvis to be just 5,472,730,538^[19] (sequence A109741 in OEIS). The On-Line Encyclopedia of Integer Sequences (OEIS) is an extensive searchable database of integer sequences, freely available on the Web. ... The class of Sudoku puzzles consists of a partially completed row-column grid of cells partitioned into N regions each of size N cells, to be filled in using a prescribed set of N distinct symbols (typically the numbers {1, ..., N}), so that each row, column and region contains exactly... Sphere symmetry group o. ... The On-Line Encyclopedia of Integer Sequences (OEIS) is an extensive searchable database of integer sequences, freely available on the Web. ...

The maximum number of givens provided while still not rendering a unique solution is four short of a full grid; if two instances of two numbers each are missing and the cells they are to occupy form the corners of an orthogonal rectangle, and exactly two of these cells are within one region, there are two ways the numbers can be assigned. Since this applies to Latin squares in general, most variants of Sudoku have the same maximum. The inverse problem—the fewest givens that render a solution unique—is unsolved, although the lowest number yet found for the standard variation without a symmetry constraint is 17, a number of which have been found by Japanese puzzle enthusiasts,^[20][21] and 18 with the givens in rotationally symmetric cells. Over 47,000 examples of Sudokus with 17 givens resulting in a unique solution are known. This article lists some unsolved problems in mathematics. ...

History

Page from La France newspaper, July 6, 1895

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 9×9 magic square with 3×3 sub-squares in 1892.^[22] 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. Image File history File links Download high resolution version (502x635, 315 KB) Summary I copied this image from a copy of the French newspaper La France, dated June 1895. ... Image File history File links Download high resolution version (502x635, 315 KB) Summary I copied this image from a copy of the French newspaper La France, dated June 1895. ... In mathematics, magic squares consist of a number of integers arranged in the form of a square in such a way that the sum of the numbers in every row, column and diagonal are the same. ...

Within three years Le Siècle's rival, La France, refined the puzzle so that it was almost a modern Sudoku. It simplified the 9×9 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 3×3 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.^[23] Ypres, 1917, in the vicinity of the Battle of Passchendaele. ...

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 from Indiana, and first published in 1979 by Dell Magazines as Number Place (the earliest known examples of modern Sudoku). Garns's 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.^[11] He died in 1989 before getting a chance to see his creation as a worldwide phenomenon.^[11] It is unclear if Garns was familiar with any of the French newspapers listed above. Will Shortz (b. ... Sudoku )   is a logic-based placement puzzle. ... For other uses, see Indiana (disambiguation). ... Dell Magazines is a company founded by George T. Delacorte Jr. ...

The puzzle was introduced in Japan by Nikoli in the paper Monthly Nikolist in April 1984^[11] 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.^[11] 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).^[10] It is now published in mainstream Japanese periodicals, such as the Asahi Shimbun. Nikoli (ニコリ) is a Japanese publisher that specializes in games and, especially, logic puzzles. ... Maki Kaji ) is the president of Nikoli Inc. ... Japanese writing Kanji Kana Hiragana Katakana Hentaigana Manyōgana Uses Furigana Okurigana Rōmaji   ) are the Chinese characters that are used in the modern Japanese logographic writing system along with hiragana (平仮名), katakana (片仮名), and the Arabic numerals. ... Asahi-OSAKA office Asahi is a common name in Japan, for other uses see Asahi. ...

Popularity in the media

In 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.^[24] 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). Wayne Gould (born 1945 in New Zealand) is a retired Hong Kong judge, most recently known for helping to popularize sudoku puzzles in the United Kingdom. ... A crossword is a word puzzle that normally takes the form of a square grid of black and white squares. ... The Times is a national newspaper published daily in the United Kingdom (and the Kingdom of Great Britain before the United Kingdom existed) since 1788 when it was known as The Daily Universal Register. ... is the 316th day of the year (317th in leap years) in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ...

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^[25]). Recognizing the different psychological appeals of easy and difficult puzzles, The Times introduced both side by side on 20 June 2005. From July 2005, Channel 4 included a daily Sudoku game in their Teletext service. On 2 August, the BBC's programme guide Radio Times featured a weekly Super Sudoku. is the 171st day of the year (172nd in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... This article is about the British television station. ... A BBC Ceefax page from January 9, 2007. ... is the 214th day of the year (215th in leap years) in the Gregorian calendar. ... Current Radio Times logo Radio Times is the BBCs weekly television and radio programme listings magazine. ...

Even the Greeks owe the publication of their first Sudoku magazine to British influence. It was at Heathrow airport in the summer of 2005 that a Greek computer magazine publisher first laid eyes on a British Sudoku magazine and - realising the opportunity - proceeded to purchase the necessary software and quickly launch the first local Sudoku magazine that became an instant success. Compupress SA: Greek publishing company formed in 1982. ...

In the United States, the first newspaper to publish a Sudoku puzzle by Wayne Gould was The Conway Daily Sun (New Hampshire), in 2004.^[26] The Conway Daily Sun is a six-day (Monday through Saturday) free daily newspaper published in the town of Conway, New Hampshire, USA, covering the Mount Washington area. ...

The world's first live TV Sudoku show, 1 July 2005, Sky One.

The world's first live TV Sudoku show, Sudoku Live, was a puzzle contest first broadcast on 1 July 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. Image File history File links SudokuLive2. ... Image File history File links SudokuLive2. ... is the 182nd day of the year (183rd in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Puzzle contests are popular competitions in which the objective is to solve a puzzle within a given time limit, and to obtain the best possible score among all players. ... is the 182nd day of the year (183rd in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... The tone or style of this article or section may not be appropriate for Wikipedia. ... Carol Jean Vorderman MBE (born 24 December 1960, Bedford), is a UK television personality best known for being a long-standing co-presenter of Channel 4 game show Countdown. ...

Later in 2005, the BBC launched SUDO-Q, a game show that combines Sudoku with general knowledge. However, it uses only 4x4 and 6x6 puzzles. For other uses, see BBC (disambiguation). ... SUDO-Q is BBC quiz show based on a mix of the number puzzle Sudoku and general knowledge questions. ... Quiz show redirects here. ...

Sudoku software is now also very popular on PCs, websites, and mobile phones. It comes with many distributions of Linux. It has also been released on portable video game handhelds such as the Nintendo DS, PlayStation Portable, the Game Boy Advance, and even on several iPod models. One of the most popular video games which features Sudoku is Brain Age: Train Your Brain in Minutes a Day!. Critically and commercially well received, it generated particular praise for its Sudoku implementation,[1][2][3] and sold more than 8 million copies worldwide.[4] NDS redirects here. ... The PlayStation Portable , officially abbreviated as PSP) is a handheld game console released and currently manufactured by Sony Computer Entertainment. ... “GBA” redirects here. ... iPod is a brand of portable media players designed and marketed by Apple and launched in October 2001. ...

Competitions

• The first world championship was held in Lucca, Italy from 10 to 12 March 2006;^[27] it was won by Jana Tylová, a 31-year-old accountant from the Czech Republic. The competition included numerous variants.^[28]
• The second world championship was held in Prague from March 28 to April 1, 2007. The individual competition was won by Thomas Snyder of the United States, with Japan winning the team contest.^[29] official WSC 2007 website
• Hosted by renowned puzzle master Will Shortz, The Philadelphia Inquirer Sudoku National Championship was the first U.S. Sudoku Championship ever. The unprecedented event was held from October 19 to 21, 2007 in Philadelphia, PA. Prizes ranging from $100 to $10,000 were awarded for a variety of categories. Solvers competed at the Beginner, Intermediate or Advanced level. The winner of the Advanced level, the aforementioned Thomas Snyder,^[30] won $10,000 and a spot on the U.S. National Sudoku Team in which he and the other members will compete in the 2008 World Sudoku Championship in India. The Philadelphia Inquirer Sudoku National Championship

Chrono Trigger character, see Lucca (Chrono Trigger). ... For other uses, see Prague (disambiguation). ... The Philadelphia Inquirer is one of a two Knight Ridder newspaper duopoly daily for the Philadelphia area. ...

See also

The class of Sudoku puzzles consists of a partially completed row-column grid of cells partitioned into N regions each of size N cells, to be filled in using a prescribed set of N distinct symbols (typically the numbers {1, ..., N}), so that each row, column and region contains exactly... A Sudoku puzzle (image hyperlinked to solution) This is a list of Sudoku terms and jargon. ... Killer sudoku (also killer su doku, sumdoku, sum doku, addoku, or samunamupure) is a puzzle that combines elements of sudoku and kakuro. ... A scrambled sudokube puzzle Sudokube is a variation on a Rubiks Cube in which each face resembles one-ninth of a Sudoku grid: the numbers from one to nine. ... A Latin square is an n × n table filled with n different symbols in such a way that each symbol occurs exactly once in each row and exactly once in each column. ... A logic puzzle is a puzzle deriving from the mathematics field of deduction. ... This is a list of major puzzles published by Nikoli. ... Easy Cross Sums puzzle The Cross Sums is a very common type of logic puzzle that is often referred to as a mathematical transliteration of the crossword. ... For the artistic activity, see Paint by number. ... Futoshiki ) or Unequal is a logic puzzle game from Japan. ...

References

Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 279th day of the year (280th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 279th day of the year (280th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 279th day of the year (280th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 279th day of the year (280th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 279th day of the year (280th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 258th day of the year (259th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 136th day of the year (137th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 212th day of the year (213th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 250th day of the year (251st in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 259th day of the year (260th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 259th day of the year (260th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 259th day of the year (260th in leap years) in the Gregorian calendar. ... is the 92nd day of the year (93rd in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 254th day of the year (255th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 319th day of the year (320th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 294th day of the year (295th in leap years) in the Gregorian calendar. ...

External links

• Sudoku at the Open Directory Project – An active listing of Sudoku links.
• Father of Sudoku puzzles next move BBC