List of Sudoku terms and jargon

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A Sudoku puzzle (image hyperlinked to solution)
A Sudoku puzzle (image hyperlinked to solution)

This is a list of Sudoku terms and jargon.

This list is incomplete; you can help by expanding it.

Contents

[edit] List organization and conventions

This list provides a brief glossary of Sudoku terminology. Items are listed thematically, and usually only once, with a brief description and possibly a link to a detailed description. Links to example usage are provided as in-line numbered references (like [1]). Here the default usage of Sudoku refers to the prominent 9×9 format, as illustrated.

In-line usage links (like[1]) and are generally not listed in the References section. Only significant content references are linked by name or cited in References. The example links ([1]) were a convenient selection. For more on link selection see the discussion page for this article.

[edit] Grid layout and puzzle terms

A Sudoku grid has 9 rows, columns and boxes each having 9 cells. The full grid has 81 cells. Cells are commonly called squares, but in technical descriptions the term square is avoided since the boxes and grid are also squares. Boxes are also known as blocks. Three vertically stacked blocks make a stack. Three horizontally connected blocks make a band. A chute is either a band or a stack. A grid has 3 bands, 3 stacks and 6 chutes.

The use of the boxes to partition the grid can be generalized to other equal sized partition shapes, in which case the sub-areas are known as regions. See Variants below. In some cases the regions are only equal sized, not equal shaped.

Rows, columns and regions are collectively referred to as units or scopes, of which the grid has 27. The One Rule can then be compactly stated as: 'Each digit appears once in each unit'.

Size refers to the size of a puzzle or grid. Often a composite row × column designation is used, e.g. size 9×9. In technical discussions size may mean the number of cells, e.g. 81. Since the number of cells in a region must be the side dimension of the square grid, e.g. 9 cells per block for a 9×9 grid, it is convenient to just use the region size, e.g. 9.

[edit] Puzzle terms

A puzzle is a partially completed grid. The initially defined values are known as givens or clues. A proper puzzle has a single (unique) solution. A proper puzzle that can be solved without trial and error (guessing) is known as a satisfactory puzzle. An irreducible puzzle (a.k.a. minimum puzzle) is a proper puzzle from which no givens can be removed leaving it a proper puzzle (with a single solution). It is possible to construct minimum puzzles with different number of givens. The minimum number of givens refers to the minimum over all proper puzzles and identifies a subset of minimum puzzles. See Mathematics of Sudoku-Minimum number of givens for values and details.

[edit] Sudoku variants

The classic 9×9 Sudoku format can be generalized to an

N×N row-column grid partitioned into N regions, where each of the N rows, columns and regions have N cells and each of the N digits occur once in each row, column or region.

This accommodates variants by region size and shape, e.g. 6 cell rectangular regions (The N×N Sudoku grid is always square). For prime N, polyominos shaped regions can be used. The requirement to use equal sized regions, or have the regions cover the grid entirely can also be relaxed.

Other variation types include additional value placement constraints, alternate cell symbols (e.g. letters), alternate mechanism for expressing the clues, and composition with overlapping grids. This page provides a simple list of variants. See Sudoku - Variants for details and additional variants.

For rectangular regions the row-column dimensions of the region may be used to describe the grid as whole, e.g. 3×2, since each of the grid side dimensions must be the product of row *column, e.g. for a 3×2 rectangular region, the grid must be 6×6. For rectangles of size N×1 or 1×N, the region is a row or column, and Sudoku becomes a Latin square.

[edit] Sudoku types and classes

Sub Doku[1] 
grid smaller than 9×9
Super Doku[2] 
grid larger than 9×9
Prime Doku[3] 
N×N grid where N is prime. Generally constructed with polyomino regions, e.g. Go Doku and pentominos.
Maximum Su Doku[4] 
the class of puzzles which have the maximum number of independent clues needed to allow a complete and unique solution.
Minimum Su Doku[5] 
the class of puzzles which have the minimum number of clues needed to allow a complete and unique solution.
Proper puzzle[6] 
a puzzle that has a unique solution.
Satisfactory puzzle[7] 
a puzzle that does not require trial and error. Note: the level of trial and error is usually not explicitly defined, see trial and error below.
purely numeric puzzle
puzzles which use purely numbers
purely literal puzzle
a sudoku puzzle which uses letters instead of numbers
numeroliteral puzzle
puzzle using a combination of letters and numbers usually seen in 12x12 sudoku puzzles

[edit] Variants by size

polyomino 
a shape composed of equal sized, side-adjacent squares. Often used for Sudoku region variants. Polyominos are named by size: (5)pentomino, (6)hexomino, (7)heptomino, (8)octomino, and (9)nonomino.
du-sum-oh[8] 
5×5, 6×6, 7×7, 8×8 or 9×9 grid with irregular, polyomino, shaped regions and minimal number of clues.

Squiggly Sudoku puzzles are also known as Latin Squares Puzzles (invented by Mark Thompson), Du-Sum-Oh, Jigsaw Sudoku, Irregular Sudoku, or Geometric Sudoku. These puzzles typically have anywhere from 5 to 9 rows. The number of rows is always equal to the number of columns. The regions are polyominos made of the same number of squares that are in any one row of the puzzle. Bob Harris created a web site called www.bumblebeagle.org, which features Squiggly Sudoku/Du-Sum-Oh puzzles. The irregularity of the regions compensates for the relatively small number of givens.

[edit] 4×4

Shi Doku[9] 
four 2×2 regions. Shi is Japanese for 4.

[edit] 5×5

Go Doku[10] 
5×5 grid with pentomino regions. Go is Japanese for 5.
Logi-5 
5×5 grid with pentomino regions

[edit] 6×6

These use 6 2×3 rectangular regions:

Roku Doku[11]
(unnamed) 
featured at the World Puzzle Championship
Sudoku X - with unique main diagonals

[edit] 7×7

(unnamed) 
7×7 grid with six heptomino regions and a disjoint region, featured at the World Puzzle Championship

[edit] 8×8

Super Sudoku X - 4 4×2 + 4 2×4 rectangular blocks

[edit] 9×9

Sudoku 
classic 9×9 grid with nine 3×3 regions
Jigsaw Sudoku 
9×9 grid with nonomino regions
du-sum-oh[12] 
5×5, 6×6, 7×7, 8×8 or 9×9 grid with irregular, polyomino, shaped regions and minimal number of clues.

Only 'One Rule' variant puzzles with simple givens are listed in this section. For variants with other clue mechanisms, see Constraint and clue variants.

[edit] 12×12

Maxi 
twelve 3×4 rectangular blocks

[edit] 16×16

Number Place Challenger 
sixteen 4×4 regions

[edit] 25×25

Sudoku the Giant
twenty-five 5×5 regions

[edit] Constraint and clue variants

Puzzles with additional constraints on the placement of values including various forms of expressing the constraints (e.g. < > relations, sums, linked cells, etc).

main diagonals unique 
the cell values along both main diagonals must be unique, see Sudoku X.
relative digit location 
digits use the same relative location within selected regions. The matching cells or regions are often color coded.

Mathematics of Sudoku has identified numerous additional constraints as analytic possibilities.

Samunamupure (clue sums) 
regions of various shapes and sizes. The usual constraints of no repeated value in any row, column or region apply. The clues are given as sums of values within regions (e.g. a 4-cell region with sum 10 must consist of values 1,2,3,4 in some order).
(unnamed) (relation clues) 
replaces region sum clues with relations: the clues are symbols =, < and > showing the relative values of (some but not all) adjacent region sums.

[edit] Terms related to solving

The meanings of most of these terms can be extended to region shapes other than blocks. To simplify reading, definitions are given only in terms of blocks or boxes.

scanning 
the process of working through a puzzle to look for or eliminate values
cross hatching 
process of elimination that checks rows and columns intersecting a block for a given value to limit the possible locations in the block
counting 
process of stepping through the values for a row, column or block to see where they can or cannot be used
box line reduction strategy 
a form of intersection removal in which candidates which must belong to a line can be ruled out as candidates in a block (or box) that intersects the line in question.
candidate 
potential value for a cell
contingency 
a condition limiting the location of a value
chain 
a sequence of contingencies connected by alternate values
higher circuits 
related locations outside the immediate row, column and grid. The locations are related by value contingencies.
independent clues 
a set of clues that cannot be deduced from each other. Often depends on the order of choosing the clues for a given grid.
intersection removal 
when any one number occurs twice or three times in just one unit (or scope) then we can remove that number from the intersection of another unit. For example, if a certain number must occur on a certain line, then occurrences of that number found in a block that intersects this line can be ruled out as candidates. Sometimes called Pointing (or matched) Pairs (or twins)/Triples (triplets) as they point out a candidate that can be removed.
trial and error 
the process of guessing successive candidate values in conjunction with deductive elimination. A.k.a.: what-if, bifurcation, garden of forking paths, depth first search, exhaustive search, back-tracking search, Ariadne's thread. Note: there is no clear boundary between trial-and-error and the use of pattern recognition strategies to eliminate values (higher circuits), the latter being a condensed form of analysis based on elimination by contradiction, i.e. the same as what-if.
nishio 
what-if method of elimination, where the use of a candidate is eliminated, that would make its other (necessary) placements impossible.
The One Rule 
fill in all (blank) cells so that each row, column and box contains the values 1-9. Same as: fill in the grid so that each row, column and box contains the values 1-9 exactly once, without changing the clues.
single[13] or singleton [14] or lone number [15] 
the only candidate in a cell
hidden single[16] 
a candidate that appears with others, but only once in a given row, column or box.
locked candidate[17] 
a candidate limited to a row or column within a block.
naked pair[18] 
2 cells in a row, column or block, which together contain only the same 2 candidates. These candidates can be excluded from other cells in the same row, column or block.
hidden pair[19] 
2 candidates that appear only in 2 cells in a row, column or block. Other candidates in those 2 cells can be eliminated.
trio [20] 
3 cells in a unit sharing 3 numbers exclusively. See triples and quads.
triples and quads 
the concepts applied to pairs can also be applied to triples and quads.
x-wing[21] 
see N-fish (with N=2).
swordfish[22] 
see N-fish (with N=3).
N-fish [23] 
analogues of hidden pairs/triples/quads/... A pattern formed by all candidate cells for some digit in N rows (or columns), that spans only N columns (rows). All other candidates for that digit in those columns (rows) can then be excluded. Names for various N-fish:
  • 2-fish : x-wing
  • 3-fish : swordfish
  • 4-fish : jellyfish
  • 5-fish : squirmbag - For 9×9 Sudoku, there's no in point naming higher-order (>4) fish, since every N-fish comes paired with a 9-N fish whose effect is the same (thus any 5-fish is paired with a jellyfish; any 6-fish with a swordfish; any 7-fish with an x-wing; any 8-fish with a hidden or naked single). Nevertheless, a 5-fish is occasionally called a squirmbag.
  • 6+ fish : 6-gronk, 7-gronk.. [24] - these patterns are only useful for Sudoku larger than 9×9.
Remote Pairs [25]
When a long string of naked pairs that leads around the grid exists, any cells that are in the intersection of the cells at the beginning and the end of the string may not be either of the numbers in the naked pairs, for example, 4 and 7.

[edit] Cell reference schemes

  • 1...81 or 0...80
  • Row & column
  • Box & cell

[edit] Math related terms

  • Latin square related puzzle with only row and column constraints.
  • constraints - rules or conditions. In Sudoku, the rule(s) requiring each digit appear once in each row, column and region.
  • triplet - the set of 3 values in a row or column within a block.

[edit] See also

[edit] References

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