I would love to know how many variations of the game sudoku are out there? Does anyone have a clue? I love the game and would like to try as many different styles to test my skills. What’s the best site play a variety of styles on?

Way to go, Thomas! If you ever get bored with Sudoku, try Alpha Sleuth sometime. :-)

Sudoku is the reason I joined this website
I can use this web to answer sudoku puzzles
That's why I LOVE THIS WEBSITE?
yahoo! hey it googles...

Jun 1st 2006, 10:22 PM
CHEATER! 00:07:41 144.60
Jun 1st 2006, 10:30 PM
CHEATER! 00:06:20 177.16
Jun 1st 2006, 10:37 PM
CHEATER! 00:06:56 267.40

I got these scores on my own, on smartprize.co.uk, but it said i cheated. what is up with the system?

Hi,
i wants to increase my creativity and inovation power.I think that this is one of the best way to make your mind upto date, through puzzels.

Is it validly SuDoku if more than one solution?
This online-playable SuDoKu was recently generated/offered at www.puzzle.ro/en/sudoku but has 3 solutions as shown:
____83__1 426783951 247683951 247683951
95_2_1__4 957261384 956271384 958271364 <(6/8)
3___457_2 381945762 318945762 316945782 <(8/6)

__5___2__ 845319276 485319276 485319276
16__57__9 162857439 162857439 162857439
_9_4__815 793426815 793426815 793426815

_7_______ 574632198 674532198 674532198
______643 219578643 521798643 521798643
___1_4_2_ 638194527 839164527 839164527

According to Wikopedia regarding SuDoku:

Variants

Although the 9x9 grid with 3x3 regions is by far the most common, numerous variations abound: sample puzzles can be 4x4 grids with 2x2 regions; 5x5 grids with pentomino regions have been published under the name Logi-5; the World Puzzle Championship has previously featured a 6x6 grid with 2x3 regions and a 7x7 grid with six heptomino regions and a disjoint region. Even the 9x9 grid is not always standard, with Ebb regularly publishing some of those with nonomino regions. Larger grids are also possible, with Dell regularly publishing 16x16-grid Number Place Challenger puzzles and Nikoli proffering 25x25 Sudoku the Giant behemoths. Another common variant is for the numbers in the main diagonals of the grid to also be required to be unique; all Dell Number Place Challenger puzzles are of this variant.

Five 9x9 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 this form of puzzle is known as Samurai Su Doku.

A three-dimensional Sudoku puzzle was invented by Dion Church and published in the Daily Telegraph in May 2005.

Alphabetical variations, which use letters rather than numbers, have also emerged. The Guardian calls these Godoku and describes them as .devilish'. Others title them Wordoku. The required letters are given beneath the puzzle. Once arranged they spell out a topical word between the top left and bottom right corners. This adds an extra dimension to Sudoku as it may be possible to guess what the word is, indicating what some of the unfilled cells might be.

Other variants common in Japanese magazines include, but are not limited to:

• Sequentially connected puzzles: several standard 9x9 puzzles are solved consecutively. Only the first puzzle has enough givens to be solved on its own; once the first puzzle is solved, one or more numbers are transferred from its solution to the starting grid of the second, etc. In some cases, the solver must work back and forth between partially completed puzzles.
• Very large puzzles made up of multiple overlapping puzzles (usually, but not always, 9x9s). Puzzles made up of 20 to 50 or more standard grids are not uncommon. The region of overlap varies x two 9x9s may share 9, 18, or 36 cells. Often, there are no givens in overlapped areas.
• Otherwise standard puzzles in which each cell is a member of four groups rather than the normal three (rows, columns, and regions): digits with the same relative location within their respective regions must not match. Such puzzles are usually printed in colour, with each disjoint group sharing one colour for clarity.
  The 2005 U.S. qualifier for the World 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 liquid crystal display.

Wikipedia, the free encyclopedia.

The goal of a Su Doku problem is to complete the published grid so that no number appears more than once in any row, column or 3x3 subgrid. To set up the solver, simply type the numbers printed into the corresponding squares in the grid below.

(The Tab and Shift-Tab keys allow the grid to be navigated without use of the mouse).

Solve - There are three solve buttons:
Solve completes the grid (provided that a solution exists).
Unsolve resets any squares on the grid filled by a previous press of the Solve button.
Reset resets the entire grid.

Evaluate - checks to see whether the current incomplete grid has a unique solution.

Labelling Format - allows the user to switch between the 'Numeric from 1' format used by the majority of sources and the 'Alphanumeric from 0' format used by the 4x4 puzzles.

The Clipboard - Copy transfers the current grid into a separate clipboard window (the system clipboard cannot be used for security reasons) in the format selected in the drop-down box on the far right of the row. The two supported formats are Plain Text and Library Book. Once Copy has been pressed, simply select the displayed grid in the clipboard window, press Ctrl-Insert to copy it, then press Shift-Insert from within some other document, such as a new e-mail message. The grid will look its best rendered in a monospaced font such as Courier. Paste performs the opposite operation, i.e. it transfers a grid from the clipboard window (which must have been previously opened by a press of the Copy button) to the solver. (Only the Plain Text format is supported by the Paste operation). Suppose you have received an e-mail that contains a Su Doku puzzle in the approved clipboard format. Select the grid from within the document, then press Ctrl-Insert in order to copy the grid to the system clipboard. Press Shift-Insert within the clipboard window to copy the text there, then press the Paste button to copy the grid from the clipboard window into the solver.

Resize - Although classical Su Doku puzzles use a 3x3 grid of boxes, the Su Doku Solver supports the alternative box grids that are sometimes seen. Use the Resize button to change the grid size. Be aware that the grid might not display properly if you use this function.

Compose - composes a fresh puzzle. The new puzzle is certain to be symmetrical, have a unique solution and feature the requested number of filled cells. Note that complicated puzzles (in the case of the classic 3x3 Su Doku puzzle, 'complicated' usually means with less than 24 filled cells) might take a considerable time to generate. Press Break in order to interrupt the procedure.

Patterns - The Patterns section dictates which patterns should be detected during the Solve phase. The numbers to the right refer (except in the case of Guess) to the total number of candidate move eliminations performed due to the discovery of each type of pattern. In the case of Guess, the figure is the total number of guesses performed.

Reasoning - The text box at the bottom displays the reasoning that has been used to solve the puzzle. Click part-way through the reasoning in order to view partial solutions.

SourceForge.net

Solution methods

The strategy for solving a puzzle may be regarded as comprising a combination of three processes: scanning, marking up, and analysing.

Scanning

Scanning is performed at the outset and periodically throughout the solution. Scans may have to be performed several times in between analysis periods. Scanning comprises two basic techniques, cross-hatching and counting, which may be used alternately:

• Cross-hatching: the scanning of rows (or columns) to identify which line in a particular region may contain a certain number by a process of elimination. This process is then repeated with the columns (or rows). For fastest results, the numbers are scanned in order of their frequency. 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 numbers. Counting based upon the last number discovered may speed up the search. It also can be the case (typically in tougher puzzles) that the value of an individual cell can be determined by counting in reverse - that is, scanning its region, row, and column for values it cannot be to see which is left.

Advanced solvers look for "contingencies" while scanning - that is, narrowing a number's location within a row, column, or region to two or three cells. When those cells all lie within the same row (or column) and region, they can be used for elimination purposes during cross-hatching and counting (Contingency example at Puzzle Japan). Particularly challenging puzzles may require multiple contingencies to be recognized, perhaps in multiple directions or even intersecting - relegating most solvers to marking up (as described below). Puzzles which can be solved by scanning alone without requiring the detection of contingencies are classified as "easy" puzzles; more difficult puzzles, by definition, cannot be solved by basic scanning alone.

Marking up

Scanning comes to a halt when no further numbers can be discovered. From this point, it is necessary to engage in some logical analysis. Many find it useful to guide this analysis by marking candidate numbers in the blank cells. There are two popular notations: subscripts and dots. In the subscript notation the candidate numbers are written in subscript in the cells. The drawback to this is that original puzzles printed in a newspaper usually are too small to accommodate more than a few digits of normal handwriting. If using the subscript notation, solvers often create a larger copy of the puzzle or employ a sharp or mechanical pencil. The second notation is a pattern of dots with a dot in the top left hand corner representing a 1 and a dot in the bottom right hand corner representing a 9. The dot notation has the advantage that it 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 easy to erase without adding to the confusion.

Analysing

There are two main analysis approaches - elimination and what-if.

• In elimination, progress is made by successively eliminating candidate numbers from one or more cells to leave just one choice. After each answer has been achieved, another scan may be performed - usually checking to see the effect of the latest number. There are a number of elimination tactics. One of the most common is "unmatched candidate deletion". Cells with identical sets of candidate numbers are said to be matched if the quantity of candidate numbers in each is equal to the number of cells containing them. For example, cells are said to be matched within a particular row, column, or region if two cells contain the same pair of candidate numbers (p,q) and no others, or if three cells contain the same triple of candidate numbers (p,q,r) and no others. These are essentially coincident contingencies. These numbers (p,q,r) appearing as candidates elsewhere in the same row, column, or region in unmatched cells can be deleted.
• In the what-if approach, a cell with only two candidate numbers is selected and a guess is made. The steps above are repeated unless a duplication is found, in which case the alternative candidate is the solution. In logical terms this is known as reductio ad absurdum. Nishio is a limited form of this approach: for each candidate for a cell, the question is posed: will entering a particular number prevent completion of the other placements of that number? If the answer if yes, then that candidate can be eliminated. The what-if approach requires a pencil and eraser. This approach may be frowned on by logical purists as too much trial and error but it can arrive at solutions fairly rapidly.

Ideally one needs to find a combination of techniques which avoids some of the drawbacks of the above elements. The counting of regions, rows, and columns can feel boring. Writing candidate numbers into empty cells can be time-consuming. The what-if approach can be confusing unless you are well organised. The Holy Grail is to find a technique which minimises counting, marking up, and rubbing out.

Wikipedia, the free encyclopedia.

Rules and terminology

The puzzle is most frequently a 9x9 grid made up of 3x3 subgrids (called "regions"). Some cells already contain numbers, known as "givens". The goal is to fill in the empty cells, one number in each, so that each column, row, and region contains the numbers 1 through 9 exactly once. Each number in the solution therefore occurs only once in each of three "directions", hence the "single numbers" implied by the puzzle's name.

The attraction of the puzzle is that the completion rules are simple, yet the line of reasoning required to reach the completion may be difficult. Published puzzles often are ranked in terms of difficulty. This also may be expressed by giving an estimated solution time. While, generally speaking, the greater the number of givens, the easier the solution, the opposite is not necessarily true. The true difficulty of the puzzle depends upon how easy it is to logically determine subsequent numbers.

Sudoku is recommended by some teachers as an exercise in logical reasoning. The level of difficulty of the puzzles can be selected to suit the class. The puzzles are often available free from published sources and also may be custom-generated using software.

Wikipedia, the free encyclopedia.