Sudoku (Japanese: 数独, sūdoku), sometimes spelled Su Doku, occurs as logic-depending placement puzzle, also referred to as Total Place in the United States. the aim of the canonical puzzle is to enter the number from either One across 9 within both cell of a 9×9 grid processed higher of Three×Three subgrids (known as "regions"), starting sustaining various number given within occasionally cells (a "givens"). Every row, column & vicinity must contain lof these one time of every number. Completing a puzzle takes patience & logical ability. Its grid layout is redolent of more newspaper puzzles such as crosswords and chess problems. Although 1st published around 1979, Sudoku at the start became popular within Japan within 1986 and attained international popularity in 2005.

Introduction

A word Sudoku means "numbers singly" in Japanese. (This title occurs as registered trademark of puzzle publisher Nikoli Co. Ltd inside Japan, & more Japanese publishers typically refer thereto when "number place". Understand History section, below.) A number around Sudoku puzzles come utilized for convenience; arithmetical relationships between number come absolutely irrelevant. Any placed of distinct symbols might launder; letters, shapes, or even colours can be utilized while forgoing altering a system (Penny Press' Scramblets and Knight Features Syndicate's Sudoku Word both have letters). Dell Magazines, the puzzle's conceiver, has been utilizing number for Total Place within its magazines since it number one published it above 25 years ago. Number come utilized throughout this article.

A attraction of a puzzle is that a completion system come elementary, eventually a line of reasoning mandatory to email the completion can be hard. Sudoku is recommended by a few teachers as an exercise in logical reasoning. A level of difficulty of a puzzles may be selected to lawsuit the audience. A puzzles come typically available loose from either promulgated sources & too can be custom-generated applying software package.

Rules and terminology
the puzzle is virtually all oftentimes a 9×9 grid manufactured higher of Three×Three subgrids (known as "regions"). A few cells already contain statistics, called "givens". A goal is to fill within a empty cells, 1 total in every, therefore that both column, row, & area contains the first–9 exactly it used to be that. Every total in the guide so occurs single once in both of tercet "directions", hence a "single numbers" tacit per puzzle's title.

Solution methods

the strategy for solving the puzzle can be regarded when comprising a combination of iii processes: scanning, marking higher, & analysing.

gay

Marking up
Scanning comes to the prevent after there is no farther prices may be found. From either this point, these are necessary to locate within a few logical analysis. Numerous buy it utile to guide this analysis by marking candidate amounts in the blank cells. There are 2 popular notations: inferior & dots. within a inferior notation a candidate statistics come written in inferior in the cells. the drawback to this is that original puzzles printed inside a newspaper unremarkably come as well little to accommodate to a higher degree two or three digits of normal handwriting. In case using the inferior even even notation, convergent thinker typically produce the big copy of the puzzle or use the sharp or mechanical pencil. The 2nd notation occurs as pattern of dots by using the dot in the top left h& corner representing the Unity and the dot in the bottom best hand corner representing the Ennead. A dot notation has a benefit that it may be utilized on the original puzzle. Sleight is compulsory in situ a dots, since lost dots or even accidental marks inevitably lead to confusion & might not become real life to erase forgoing adding to the confusion. Applying the pencil would so become recommended.

Analysing

2 independent analysis approaches come "elimination" & "what-if".

Around elimination, progress is mass produced by in turn eliminating candidate amounts from either a single or even supplementary cells to leave good a single selection. When apiece guide has been achieved, an additional market scanner can be performed — unremarkably checking to understand a outcome of the latest total. There are a total of elimination maneuver, completely of which are then according to the elementary system given above, which develop significant & utile corollaries, including:

1. The givenorth placed of n cells inorth any particular prevent, row, or even column may just accommodate n different figures. This is the basis for the "unmatched candidate deletion" system, discussed following.

2. Both placed of candidate cost, One-9, must finally exist as within an independently self-consistent pattern. This is the basis for advanced analysis techniques that postulate review of the entire placed of possibilities for the given candidate total. Single certain "closed circuit" or evenorth "n×n grid" possibilities survive (which keep around acquired peculiar list like "X-wing" & "Swordfish", among others). In case these system may exist as identified, elimination of candidate possibilities external to the grid framework could another time be achieved.

One of a usual elimination manoeuvre is "unmatched candidate deletion". Cells using monovular sets of candidate counts come said to become matched whenever a quantity of candidate counts around every is capable the total of cells containing the babies; fundamentally, which are actually perfectly coincident contingencies. For even even instance, cells come said to exist as matched in a particular row, column, or vicinity (scope) in case 2 cells contain a equivalent pair of candidate statistics (p,q) & there is there are no others, or in case terzetto cells contain the equivalent triplet of candidate cost (p,q,r) & no others. a placement one counts anywhere else inside the matching scope would produce a guide for even the matched cells impossible; so, the candidate counts (p,q,r) appearing in unmatched cells in the row, column or region scope may be deleted. This principle likewise works sustaining candidate dull subsets — in case trine cells st& candidates (p,q,r), (p,q), & (q,r) or good (p,r), (q,r), and (p,q), tons of the placed (p,q,r) elsewhere in the scope may be deleted. A principle is avowedly for completely quantities of candidate statistics.

Another related principle is likewise avowedly — whenever a total of cells (withwithin the row, column or even vicinity scope) in which a placed of candidate figures merely come out is up to the quantity of candidate figures, the cells & cost come matched & just victims totals could come out in matched cells. More candidates in the matched cells may be eliminated. For instance, inside case (p,q) may lone come out in Ii cells (inside the specific row, column, area scope), more candidates in the Ii cells may be eliminated. A foremost principle is according to cells in which single matched totals pop up. A 2nd is according to totals that pop up exclusively inside matched cells. Advanced techniques carry these conception farther to include multiple rows, columns, & interferes. (View "X-wing" & "Swordfish", above.)

In the what-in case approach, the cell by owning simply ii candidate statistics is selected, & the believe is mass produced. a steps above come repeated unless the duplication is encountered or even a cell is left sustaining there is no imaginable candidate, where example the guide candidate is the guide. Inside logical terms, this is referred to as reductio ad absurdum. Nishio is the limited form of this approach: forEvery candidate for a cell, the wonder is posed: might typing a particular total block completion of the more placements of that total? Whenever a guide is yes, so that candidate may be eliminated. the what-whenever approach takes a pencil & eraser. This approach can be frowned in by logical purists when trial and error (and virtually all promulgated puzzles come built to assure that it may never exist as necessary to resort to this manoeuvre,) however it may reach solutions fairly quickly.

Ideally 1 needs to call for the combination of techniques which avoids a select few of the drawbacks of the above elements. A count of regions, rows, & columns potty sense irksome. Writing candidate statistics into empty cells may be instance-ingesting. A what-whenever approach may be confusing unless your family is swell organised. A proverbial Holy Grail is to find the system which minimises counting, marking higher, & rubbing retired.

Computer solutions
For computer programmers, coding the research for cell values depending elimination, contingencies & multiple contingencies ( compulsory for harder Sudoku) is comparatively straightforward. These computer program emulate the mortal logic to solve a puzzle forgoing resorting to guesses. Given a self-genus euthynnus constraints of virtually all Sudoku publishers, this method usually succeeds.

These are too fairly elementary to build the backtracking search. Generally this involves assigning a value (say, One, or even a nighest available total to Single) to a number one available cell (say, the top left hand corner) and so progress to assign the next available value (say, Ii) to the next available cell. This continues until a conflict occurs, where example the next guide value is utilized for the go cell changed. In case a cell just can not exist as filled, a program backs higher a single level (from either that cell) & attempts a next value at a higher level (hence the title backtracking). Although far from either computationally effective, this method might buy the guide, given sufficient computation instance. The standard 9×9 puzzle potty usually exist as "solved" inside of these or even ii seconds around the modern residence computer heading this algorithmic rule in an taken language, like Perl, and good deal less within the compiled language. a extrthe effective program can keep track of likely values for cells, eliminating impossible values until l1 one value remains for a cell, so filling that cell around & utilizing that data for further eliminations, then in until the puzzle is solved.

A second guide utilizes finite domain constraint programming. a constraint program specifies a constraints of the puzzle (the fact that both total inside every row, both column, & each Three×Three region must become unique, & a provided "givens"); the finite domain convergent thinker applies the constraints in turn to narrow down the guide space until a guide is observed. Backtracking can exist as applied whilst surrogate values can't otherwise be excluded.

The extremely effective way of solving such constraint problems is the Dancing Links Algorithm, by Donald Knuth. This method may be directly applied to solving Sudoku problems, counting entirely imaginable solutions for virtually all puzzles around msec. This is the method today favorite by several Sudoku computer programmer, primarily by virtue of its speed. The in no time problem solver is normally needed for virtually all test-&-error puzzle-creation algorithmic program.

Difficulty ratings

Promulgated puzzles typically come ranked inside terms of difficulty. A difficulty of the puzzle devolve on how else convenient these are to logically determine subsequent totals. Maybe amazingly, the total of givens has little or even there are no bearing in a puzzle's difficulty. Puzzles by using a minimal total of givens may become super real life to solve, & puzzles by owning to a higher degree the typical total of givens might however be pleasantly hard to solve.

Computer convergent thinker may estimate a difficulty for a human being to call for a guide, according to the complexness of the system compulsory per computer. This estimation is unremarkably precise, letting publishers to rate their Sudoku puzzles for the best nature and severity of audience. A few low versions offer many difficulty levels.

There are numbers of factors that influence the difficulty of a Sudoku puzzle. The standard formula allow quadruplet factors:

Total of fillable squares. Total of squares noticed using the run of elimination. Total of guesses that got to exist as done to email a guide. Total of backtraces performed sequentially to solve a puzzle.

A number one 2 factors come veto: a higher it is, a lower berth a difficulty is. A previous deuce factors come caring, & it increase a puzzle difficulty.

Construction
These are unremarkably believed that Dell Number Place puzzles are computer-generated; it usually keep around assibilate Xxx givens situated within an apparently random scatter, occasionally of which could even exist as deduced from either more givens. It as well use there is no authoring credits — that is, a title of the builder is non printed by owning any puzzle. Wei-Hwa Huang claims that he was commissioned by Dell to write a Total Place puzzle generator in the wintertime of 2000; before that, he was told, the puzzles were hand-hand-crafted. A puzzle generator was written sustaining Visual C++, and although it experienced choices to generate the extra Japanese-style puzzle, by owning symmetry constraints and fewer numbers, Dell opted does'nt to utilise people features. Presumptively a puzzles since so however utilize that program, although these are difficult to tell.

Nikoli Sudoku come hand-constructed, sustaining andy skinner existence credited beside every puzzle; the givens are universally uncovered within a proportionate pattern. (Building the Sudoku by owning proportionate givens may be achieved by determining ahead in which a givens is placed, & single assigning an actual total to the two equally required.) Dell Total Place Challenger (look at Variants in the image below) puzzles as well names creator credits. A Sudoku puzzles printed inside virtually all UK newspapers come apparently computer-generated however use proportionate givens, implying the further human-centered algorithmic rule; The Guardian claims its puzzles are hand-constructed "in Japan" (it is, as a matter of fact, created per foremost Japanese Sudoku setters at Nikoli) though it doesn't include authoring credits. A Shielder famously claimed that because it were hand-constructed, their puzzles would contain "imperceptible witticisms" that would be super unbelievable around computer-generated Sudoku.

These are imaginable to placed starting grids by using supplementary than of these guide & to placed grids sustaining there are no guide, however such are non considered proper Sudoku puzzles; prefer virtually all more pure-logic puzzles, the unique guide is potential. Awesome caution is involved around constructing the Sudoku puzzle, when failing to recognize inside which the total may be logically deduced at any point in construction — disregarding of how else tortuous that logic could be — can effect around an insolvable puzzle once shaping the first given contradicts what has already been built.

Whenever an effective problem solver is available, there is the super elementary method of automatic construction: arbitrarily add the digit to the grid, then search a guide. In case there is no guide is incurred, dislodge a digit & try a second. Whenever the guide is noticed, search the different guide. Whenever no more guide, a starting grid is complete; otherwise, repeat this run.

Variants

Although a 9×9 grid by having Three×Three regions is by far a usual, many variations abound: sample puzzles may be Four×Four grids by using Two×Two regions; Five×Five grids sustaining pentomino regions have been published under a title Logi-Five; the World Puzzle Championship has previously featured the 6×6 grid by owning Two×Three regions & the 7×7 grid by having half a dozen heptomino regions and the disjoint region. Possibly a 9×9 grid is non universally standard, by owning Ebb regularly publishing some of victims using nonomino regions. Big grids come besides conceivable, by having Dell regularly publishing 16×16-grid Total Place Challenger puzzles & Nikoli proffering 25×25 Sudoku a Elephantine behemoths. An additional most common variant is for a totals in the principal diagonal of the grid to as well exist as expected to become unique; the aforesaid Total Place Challenger puzzles come everthing of this variant, when come a Sudoku 10 puzzles in the Daily Mail, which use 6×6 grids. A Daily Mail as well features Extremely Sudoku X within its Weekend magazine: an 8×8 grid where rows, columns, principal diagonal, Two×Four deflects & Four×Two bars contain both total when.

5 9×9 grids which overlap at the corner regions in the shape of a quincunx is known in Japan when Gattai Five (5 incorporated) Sudoku. In The Times this form of puzzle is known as Samurai Su Doku. [http://sudoku.top-notch.co.uk/gattai5.asp]

The 3-cubic Sudoku puzzle was invented by Dion Church & published within the Daily Telegraph in May 2005.

Alphabetical variations, which stand letters like than amounts, have as well emerged. A Shielder calls these Godoku & describes the two when "devilish". Knight Features utilizes a term Sudoku Word [http://www.knightfeatures.com/KFWeb/content/features/kffeatures/puzzlesandcrosswords/KF/Sudoko/sudoku_word.html]. Around Top Notch's Wordoku [http://sudoku.top-notch.co.uk/wordoku.asp] a expected letters come given below a puzzle - another time intended it spell out a topical word between the top left & bottom perfect corners. This adds an additional dimension to Sudoku when it can exist as conceivable to believe what a word is, indicating what a few of the unfilled cells will be.

A Code Doku[http://www.mathrec.org/sudoku] devised by Steve Schaefer has an entire phrase embedded into a puzzle when a Very Wordoku[http://sudoku.top-notch.co.uk/superwordoku.asp] from either Top Notch embeds 2 9-letter words, 1 in every diagonal. These are debatable when to whether a Very Wordoku puzzles & a select few (but not 100%) of the Code Doku puzzles come avowedly Sudoku puzzles, because although it have a only valid guide, it just can't become solved completely by Sudoku logic, & a convergent thinker must depend on deducing a embedded words. Top Notch claim this as a feature designed to kill convergent thinker computer software.

Kokonotsu (the 9-letter Japanese word that just means nine) has been dubbed "SuperSudoku" by its creators. It adds dimensions & challenges non encountered within average Sudoku. When generic Sudoku puzzles lone need a streaming video player to fill around rows, columns & Three×Three boxes, Kokonotsu adds Quaternary & Fifth dimensions: them diagonals & the "Magic Puzzle Heart" consisting too of nine cost that players could locate & apply to help a two solve the puzzle supplementary quickly.

More variants green within Japanese magazines include, however are non limited to:

Consecutive attached puzzles: many standard 9×9 puzzles come solved consecutively. Sole a foremost puzzle has plenty givens to become solved in its have; another time a number 1 puzzle is solved, one or even further totals come transferred from either its guide to the starting grid of the 2nd, etc. Inside occasionally lawsuits, a problem solver must function back & forth between part completed puzzles. Super big puzzles processed higher of multiple overlapping puzzles (ordinarily, but not universally, Ennead×9s). Puzzles manufactured higher of 20 to 50 or even supplementary standard grids are non rare. A vicinity of overlap varies — both 9×9s might part Ix, Eighteen, or even 36 cells. Typically, no givens around overlapped areas. Otherwise standard puzzles where to each one cell occurs as member of quatern groups like than a normal troika (rows, columns, & regions): digits by using a equivalent proportional location inside their several regions must non match. Such puzzles come unremarkably printed inside colour, by having to each of these disjoint class action sharing one colour for clarity.

A 2005 U.S. qualifier for the Globe Puzzle Championship includes the variant known as Digital Total Place: like than givens, virtually all cells contain the unfair given — the section of a total, by using the statistics drawn when whenever a share of a seven-segment display.

In 31 August 2005, The Days began publishing what it branded when Killer Su Doku, or even Samunamupure (meaning total dull place), in which instead of personal starting cost, squares come grouped & a total of the values is given, adding an additional layer of complexness & farther dependencies to track, although it can as well help, by providing farther constraints on the statistics that may be situated. Aside from either this a normal Sudoku system use. Convenient versions own "groups" of a single square, which is au fond rendering a value, when within standard Sudoku.

Mathematics of Sudoku

A general condition of solving Sudoku puzzles inorth n^Deuce tenorth n^Two boards of north 10 north hinders is known to exist as NP-complete [http://www.phil.uu.nl/~oostrom/cki20/02-03/japansepuzzles/ASP.pdf]. This gives occasionally indication of how come Sudoku is hard to solve, although in boards of finite size the condition is finite & may be solved by a deterministic finite automaton that knows the entire game tree.

Solving Sudoku puzzles may be expressed as a graph colouring problem. the aim of the puzzle within its standard form is to construct the proper 9-colouring of the particular graphical record, given a unfair 9-colouring. A graphical record around wonder has 81 vertices, a single vertex for both cell of the grid. A vertices may be labelled sustaining a regulated pairs $(x,\backslash ,\; y)$, in which x & y come whole number between One & 9. Therein out break, 2 distinct vertices labelled by $(x,\backslash ,\; y)$ & $(x\text{'},\backslash ,\; y\text{'})$ come joined by an edge in case & single in case: $x\; =\; x\text{'}\backslash ,$ or even, $y\; =\; y\text{'}\backslash ,$ or even, $\backslash lceil\; x/3\; \backslash rceil\; =\; \backslash lceil\; 10\text{'}/3\; \backslash rceil$ & $\backslash lceil\; y/3\; \backslash rceil\; =\; \backslash lceil\; y\text{'}/3\; \backslash rceil$ A puzzle is so completed by assigning an whole number between One & 9 to every vertex, around such how else that vertices that come joined by an edge don't stand a equivalent whole number assigned to the children.

The valid Sudoku guide grid is besides the Latin square. There are significantly fewer valid Sudoku guide grids than Latin squares because Sudoku imposes a extra regional constraint. Withal, a total of valid Sudoku guide grids for the standard 9×9 grid was estimated by Bertram Felgenhauer inside 2005 to exist as 6,670,903,752,021,072,936,960 [http://www.shef.ac.uk/~pm1afj/sudoku/] . A total of valid Sudoku guide grids for the 16×16 derivation is non known.

a maximal total of givens that may be provided when however non giving a guide unique, disregarding of variation, is quatern short of a fully grid; in case deuce cases of deuce totals for each a single come missing & a cells it is to occupy come a corners of an orthogonal rectangle, & exactly 2 one cells come inside one area, there are 2 ways the statistics may be added. A opposite of this — the fewest givens that render a guide unique — is an unsolved problem, although the last total however detected for the standard variation while forgoing the symmetry constraint is Seventeen, the total of which use been encountered by Japanese puzzle enthusiasts [http://www2.ic-net.or.jp/~takaken/auto/guest/bbs46.html] [http://www.csse.uwa.edu.au/~gordon/sudokumin.php], and Eighteen sustaining a givens inside rotationally symmetrical cells.

For supplementary outcomes & conjectures, understand a Mathematics of Sudoku page.

History

Originally known as just Total Place, the foremost puzzle was created by Howard Garns, a mercenary puzzle builder, around 1979. A puzzle was 1st published within New York in the late 1970s by the specialist puzzle publisher Dell Magazines in its magazine Dell Pencil Puzzles and Word Games, under a title Total Place. A puzzle was introduced within Japan by Nikoli in the paper Monthly Nikolist in April 1984 as "Sūji wa dokushin ni kagiru (数字は独身に限る)", which may be translated when "the numbers must be single" or even "the numbers must occur only once" (独身 literally means "single; celibate; unmarried"). A puzzle was known as by Kaji Maki (鍜治 真起), a president of Nikoli. At a late date, the title was abbreviated to Sudoku (数独, pronounced sue-run-koo; sū = total, doku = lone); these are a most common practice inside Japanese to choose only the number one kanji of compound words to form a shorter version. Inside 1986, Nikoli introduced deuce innovations which guaranteed a popularity of a puzzle: the total of givens was restricted to those days are gone than Thirty & puzzles became "symmetrical" (meaning a givens were distributed around rotationally symmetrical cells). These are currently promulgated inside mainstream Japanese periodicals, like a Asahi Shimbun. Inside Japan, Nikoli however holds a trademark for the title Sudoku; more publications within Japan utilise guide list.

Around 1989, Loadstar/Softdisk Publishing published DigitHunt on the Commodore 64, which was apparently the number one residence computer version of Sudoku. At least [http://www.coregames.com/DPS3.htm one publisher] however utilizes that title.

Yoshimitsu Kanai published his computerised puzzle generator under a title Lone Total (a English translation of 'sūdoku') for the Apple Macintosh [http://www.mathsisfun.net/SingleNumber.sit] in 1995 within Japanese & English, and in 1996 for the Palm (PDA) [http://www.mathsisfun.net/SingleNumber.prc].

Bringing a run good-circle, Dell Magazines, which publishes the original Total Place puzzle, okay, as well publishes deuce Sudoku magazines: Original Sudoku & Extreme Sudoku. In addition, Kappa reprints Nikoli Sudoku in GAMES Magazine under the title Squared Away; a New York Post, USA Today, and San Francisco Chronicle now also publish a puzzle. These are besides typically involved within puzzle anthologies, like The Giant 1001 Puzzle Book (under a title Nine Figures).

Popularity in the media

Within 1997, retired Hong Kong judge Wayne Gould, 59, a New Zealander, was enticed by seeing the part completed puzzle around a Japanese bookstore. He went in to prepare the programme to make puzzles quickly; this took concluded sise years. Caring that British newspapers have a long history of publishing crosswords and other puzzles, he promoted Sudoku to The Days within Britain, which launched it in 12 November 2004. A puzzles by Pappocom, Gould's software system home, use been printed day-after-day in the Days ever since.

3 years late A Daily Mail began to publish a puzzle under a title "Codenumber". A Daily Telegraph introduced its 1st Sudoku by its puzzle compiler Michael Mepham in 19 January 2005 and other Telegraph Class action newspapers took it higher super quickly. Nationwide News Pty Ltd began publishing a puzzle in The Daily Telegraph of Sydney on 20 May 2005; five puzzles by having solutions were printed that day. A vast surge within popularity of Sudoku withwithin British newspapers & internationally hwhen led thereto existence dubbed in a globe media in 2005 multifariously as "the Rubik's cube of the 21st century" or the "fastest growing puzzle in the world".

No doubt that it was non until A Daily Telegraph introduced the puzzle in a every day basis in 23 February 2005 with a fully front-document coarse of action advertising a fact, that the more UK national newspapers began to require really interest. A Telegraphy continued to splash a puzzle in its front site, realizing that it was gaining sales only by its presence. Until so a Days got saved super quietly all about a brobdingnagian every day interest that its day-after-day Sudoku competition experienced aroused. That newspaper already got plans for do you need their market lead, & the number 1 Sudoku book was already on the equities prior to any of the more national papers got realised upright how else popular Sudoku will become.

By April & Might 2005 a puzzle experienced get popular around these publications & it was chop-chop introduced to many more national British newspapers including The Independent, The Guardian, The Sun (where it was labelled Sun Doku), & The Daily Mirror. When a title Sudoku became easily-known within Britain, a Daily Mail adopted it in situ of its earliest title "Codenumber". Newspapers competed to promote their Sudoku puzzles, by using A Days & a Daily Mail both claiming to develop been a number one to feature Sudoku, & A Defender claiming (though perhaps ironically) that its hand-hand-crafted puzzles, licensed from either Nikoli, offered a superior case (complete by using "almost imperceptible witticisms") to the computer-generated grids uncovered inside more papers.

A rapid rise of Sudoku from either proportional obscurity withwithin Britain to the front-site feature in national newspapers attracted comment in the media (look at Information in the image below) & parody (like while A Tutelary's G2 division advertised itself when the 1st newspaper supplement by using a Sudoku grid in each web page [http://www.guardian.co.uk/g2/story/0,,1482817,00.html]). Sudoku became particularly large within newspapers shortly fallowing a 2005 general election leading some commentators to indicate that it was filling a gaps antecedently occupied bye election coverage. a simpler explanation is that the puzzle attracts & retains readers — Sudoku players report an increasing feel of satisfaction as a puzzle approaches completion. Recognizing a different psychological appeals of easily & hard puzzles The Times introduced both side by side in 20 June 2005. From either July 2005 Channel 4 included a day-after-day Sudoku game in their Teletext service (at page 142).

As a 1-off, the world's number 1 survive TV Sudoku indicate, Sudoku Survive, was broadcast in 1 July 2005 on Sky One. It was presented by Carol Vorderman. Nine teams of nine players (by owning 1 celebrity in each team) representing geographical regions competed to solve the puzzle. For each one streaming video player got the hand-handheld device for typing cost corresponding to account quaternion cells. Conferring was permitted although a deficiency of acquaintance of the players by using both more inhibited an analytical discussion. the audience home was within a separate interactional competition. The Sky 1 [http://www.skyone.co.uk/programme/pgefeature.aspx?pid=48&fid=129 publicity stunt] to promote a programme by owning the world's big Sudoku puzzle went awry whilst a 275 foot (84 m) square puzzle was witnessed to stand 1,905 right solutions. the puzzle was carved into a hillside inside Chipping Sodbury, near Bristol, England, in review of the M4 motorway.