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Questions tagged [sudoku]

A Sudoku is a puzzle consisting of a grid to be filled with symbols, such that each constraining unit contains each symbol exactly once.

The typical example is a 9x9 square to be filled with the numbers 1 to 9, where the constraining units are rows, columns, and 3x3 blocks.

A Sudoku is a puzzle consisting of a grid of cells to be filled with symbols, such that each constraining unit of the grid contains each symbol exactly once.

The typical Sudoku is a 9x9 square to be filled with the numbers 1 to 9, with the constraining units being rows, columns, and 3x3 blocks. Some cells already have a value - these are called clues, or givens.

A proper Sudoku has a unique solution. A satisfactory Sudoku is a proper Sudoku that needs no trial and error to reach that solution.

Other popular variants include:

  • Killer - there are cages around cells that tell the sum of the cage
  • X-factor - on each of the two main diagonals the symbols must also be distinct
  • Shape - other shapes are used instead of blocks
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Are there published Sudoku puzzles that require guessing?

I believe in a number of books I have read and solved myself, the introduction stated that guessing should never be necessary for any of the puzzles in the book. Instead, a handful of techniques could be used to solve the puzzle completely,…
demongolem
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This is a crossudoku

So, this is a crossudoku. It is the same as a sudoku - same rules apply. However, you have been given crossword-like clues for part of the numbers on the grid. Some of the clues may have multiple answers - so you may need to be solving the…
Maria Ivanova
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Ever heard of a W-Sudoku?

You may have heard of a type of Sudoku called an XV-Sudoku. In such a Sudoku, cells connected with an "X" must sum to 10 and cells connected with a "V" must sum to 5. In this W-Sudoku (W is right between V and X), cells connected with a "W" must sum…
Jens
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There is a reason sudoku uses squares

There exists a 9x9 grid with the cells in one single row numbered 1-9 in order. The cells in the other 8 rows are initially empty. Note: The cells initially containing numbers can be in any one row; not necessarily the first. Draw borders to…
kaine
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How do I solve the world's hardest sudoku?

This question is posted under the guidelines Don't worry too hard about restricting or regulating anything that isn't turning into a problem yet. If you don't agree that this question is on topic, please go to that meta thread and talk about why you…
durron597
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Can a standard Sudoku puzzle contain a miniature Sudoku puzzle?

The following is an example of "Miniature 4x4 Sudoku puzzle" in which the goal is to fill each empty square with a number (1, 2, 3 or 4) so that there are no duplicated numbers in any row, column or 2x2 block. The solution (as a 4x4 matrix) to the…
Will Octagon Gibson
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Do sudoku answers always have a single minimal clue set?

Suppose we have a solved sudoku, which was started from a minimal set of clues to its unique solution, i.e. 17+ numbers in specific locations, which we'll call set1. Is there a set2, (or set3, etc.), with few or no elements in common with set1? Put…
agc
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Why is this considered to be "The World's Hardest Sudoku"?

NOTE: This is in reference to an existing question which I feel is poor and off-topic. In the spirit of "shaping the site while in private beta", I wanted show how the question can be re-phrased and "fixed" in order to be more on-topic here. There…
IQAndreas
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Minimum number of clues for a sudoku puzzle

In a sudoku puzzle, what is the absolute minimum number of clues that must be given to specify a layout with a unique solution? Is one in each row, column, and box (9 total) necessary or sufficient?
Kevin
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How can I spot an X-Wing?

I was doing a Sudoku puzzle (in my morning newspaper on the train to work) and got stuck at this point: _ _ _ _ 4 _ 7 2 1 4 _ 2 6 _ 7 _ 8 9 7 _ _ 8 _ 2 _ _ _ 2 9 5 4 6 8 _ _ 7 3 4 6 5 7 1 8 9 2 8 _ _ _ _ 9 6 4 5 _ 2 _ 7…
ClickRick
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How many minimal-clue sudoku puzzles are there?

It is known that there are a minimum of 17 clues needed to create a proper sudoku puzzle. For how many puzzles is 17 sufficient? From the history of the minimal proof, I gather that there are multiple puzzles for which 17 clues are enough for a…
Kevin
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What is the maximum number of empty 3x3 blocks a proper Sudoku can have?

It is possible to have a proper Sudoku with one empty block (consisting of 3x3 cells). The trivial (and very boring) example would be a puzzle where all other cells are given. It's impossible to have a proper Sudoku with an empty chute (a band of 3…
SQB
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Sudoku medium difficulty help

I keep getting stuck on the NY Times Sudoku medium difficulty puzzles. I go through one number at a time and narrow down large box where that number can only be in two spaces. When I finish the nines I start back at the ones using the information…
tazboy
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Consecutive Sudoku 6x6

I honestly don't know how to start... so I'm just looking for how to start, ie is there a number that we know where it has to go and why? In addition to standard Sudoku rules, numbers on either side of bars must be consecutive AND numbers without…
josf
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How do I solve this sudoku without guessing

I am fairly new to Sudoku and couldn't find how to progress with this one without guessing.
HyperX
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