Linux Command Library

# sudoku

#### sudoku board game

(play the game)

sudoku [options] ... [<filename>]

(generate boards)

sudoku -g [<num>] [options] ...

(solve boards)

sudoku -v [options] ...

(calculate statistics)

sudoku -s [options] ...

The sudoku board game is played on a 9x9 grid, divided into rows, columns, and 9 blocks of 3x3 squares. The objective is to fill the empty squares with the digits 1-9, so that each row, column, and block contains each of the digits 1-9 (and hence, it is not possible for any digit to appear twice in the same row, column or block).

Consider the following board, and the squares marked `a'-`h' and `x':

5 . a | 6 b 1 | . . . The digits appearing in each of the 7 9 . | . . . | c 6 8 squares `a'-`h' can be uniquely d 3 . | . 8 . | 7 . . determined. For example, the value -------+-------+------- at `a' must be 8, since an 8 appears . 5 . | 4 1 e | . . 2 in the other rows and columns of the . . 1 | f x . | 6 . . block. Using similar logic, it must 8 . . | . 3 7 | . 4 . be true that: -------+-------+------- b = 7 f = 8 . . 4 | . 9 . | g 2 . c = 1 g = 8 2 8 h | . . . | . 9 7 d = 1 h = 5 . . . | 5 i 8 | . . 6 e = 6 i = 2

In contrast, it is not possible to uniquely determine the value of `x' with the given information - it could take either the value 2 or 5. The board now contains the squares:

5 . 8 | 6 7 1 | . . . It is now possible to determine the values 7 9 . | . . . | 1 6 8 appearing in other empty squares. 1 3 . | . 8 . | 7 . . -------+-------+------- . 5 . | 4 1 6 | . . 2 . . 1 | 8 x . | 6 . . <<< the value of x must now be 5. 8 . . | . 3 7 | . 4 . -------+-------+------- . . 4 | . 9 . | 8 2 . 2 8 5 | . . . | . 9 7 . . . | 5 2 8 | . . 6

Repeating this process a few more times reveals the solution:

5 4 8 | 6 7 1 | 2 3 9 7 9 2 | 3 4 5 | 1 6 8 1 3 6 | 9 8 2 | 7 5 4 -------+-------+------- 3 5 7 | 4 1 6 | 9 8 2 4 2 1 | 8 5 9 | 6 7 3 8 6 9 | 2 3 7 | 5 4 1 -------+-------+------- 6 1 4 | 7 9 3 | 8 2 5 2 8 5 | 1 6 4 | 3 9 7 9 7 3 | 5 2 8 | 4 1 6

The sudoku game has a simple text interface (using the curses(3) library). The board is displayed in the middle of the screen, along with a summary of the allowed key presses. The cursor can be moved around the board using the arrow keys or the standard vi(1) movement keys, and each square (except for the fixed board squares that are initially revealed) can be set to a given digit by pressing the corresponding number key, or cleared by pressing either the `0' or `.' keys.

### Generating a New Board

A new board can be generated at any time by pressing the `n' key, and either a precanned or randomly generated board will be displayed. If the -n command line option is set, then only precanned boards will be displayed.

### Entering a Custom Board

A custom board (e.g. found on the internet, or published in a newspaper) can be entered into the game by first clearing the current board (press the `c' key), entering the published squares (using the cursor motion keys and entering the appropriate numbers), and then fixing the squares by pressing the `f' key. At this point, the entered squares will be fixed (and cannot be changed).

### Hints

The interactive game provides a simple hint mechanism to provide assistance in solving the board. It attempts to highlight areas of the board where moves can be made. If repeated hints are requested, the system starts revealing the digit that can be placed on the board.

A new hint can be requested by pressing the `?' key.

Often the hints can be quite cryptic. For example, consider the board below:

v v v

. . 7 | . . 9 | . . . 9 . 6 | 7 4 . | . 1 5 . . 2 | 5 1 . | . . . -------+-------+------- > 6 . 5 | . 7 . | . . 8 < The characters ><v^ highlight the > . 7 . | . . . | . 3 . < area of the hint > 8 . . | . . . | 7 . 6 < -------+-------+------- . . . | . 6 7 | 8 . . 7 4 . | . 5 . | 9 6 2 . 6 . | 4 . . | . . .

^ ^ ^

The system gives the hint `try the digit 3', but it is certainly not obvious, with the revealed squares, where the 3 goes.

-c<class>
Generate a board until it finds a board of the specified class. Supported classes are: very easy, easy, medium, hard, and fiendish.
-d
Describe the moves needed to solve the board. Can only be used with the -v option for solving precanned boards.
-f<format>
Set output format. The supported formats are:
` standard Default text format; std is a shortcut. compact Compact text format. csv Comma separated values, suitable for importing into a spreadsheet. postscript ps is a shortcut. html Simple HTML. `
-g[<num>]
Generate <num> boards (or just 1 board, if not specified) and write them to standard output.
-n
No random boards generated in the interactive game. Requires the optional file of precanned boards to be specified.
-r
Run in restricted mode, disallowing any games to be saved.
-s
Calculate statistics for the precanned boards, and attempt to classify the difficulty of solving the boards. Can be used with the -v option.
-t<filename>
Set the template file. The file set on the command line will be used instead of the default template file.
-v
Solve precanned boards, writing the solution to standard output.
<filename>
Name of the optional file containing precanned boards.
-w
Write default template to the working directory if it doesn't exist yet.

No environment variables are used directly by the sudoku program.

/usr/share/sudoku/template
Template file for generating new sudoku boards.
/usr/share/sudoku/precanned
Optional file, containing `precanned' sudoku boards.

### /usr/share/sudoku/template

The template file contains a sequence of patterns that are used for generating new sudoku boards. Each pattern is started by a line with a leading `%' character, and consists of 9 lines of 9 characters. The character `.' represents a square that is initially blank, and the character `*' represents a square with a digit that is initially displayed.

### Compact text format

This format is similar to that of the template file, but contains representations of game boards. Each board is started by a line with a leading `%' character, followed by an optional title for the board that is displayed when the game is played. This is followed by 9 lines of 9 characters, where the character `.' represents an initially empty square, and the characters `1'-`9' give the value of a fixed board square that is initially displayed. The sudoku program can read precanned files in this format, and will write them when the -fcompact option is set.

### Standard text format

This format is very similar to the compact text format, but includes additional characters to delimit the blocks in the board. The sudoku program can read precanned files in this format, and writes them by default, unless another output format is set by the -f option.

### Comma separated text format

This format is useful for importing sudoku boards into a spreadsheet. It represents each board by 9 lines of comma separated fields. Each field is blank, or contains a digit. The sudoku program cannot read precanned files in this format, and writes them when the -fcsv option is set. Unlike the standard or compact text formats, there are no lines separating boards, and hence, it is really only feasible to store one board per file.

### Postscript format

This format is useful for printing out sudoku boards. The sudoku program cannot read boards stored in this format, and writes them when the -fpostscript option is set. Unlike the standard or compact text formats, it is not possible to store multiple boards in the same file.

### HTML format

This format is useful for printing out sudoku boards. The sudoku program cannot read boards stored in this format, and writes them when the -fhtml option is set. Unlike the standard or compact text formats, it is not possible to store multiple boards in the same file.

There are a large number of websites dedicated to the sudoku puzzle that can be found easily using a search engine. Some of these sites provide game boards that can be challenging to solve, and others provide strategies for finding moves.

There are limited diagnostics available when an error occurs.

Mark Foreman for the HTML output format; Joanna Ferris and Heather for encouraging this endeavour.

Michael Kennett (mike@laurasia.com.au)

This manual page, and all associated files, have been placed into the public domain by Michael Kennett, July 2005. They may be used by anybody for any purpose whatsoever, however NO WARRANTY, of any sort, applies to this work.

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