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Sudoku Manual

1. Introduction

Sudoku is an application to generate and play the popular Sudoku logic puzzle (also known as Number Place).

The rules of Sudoku are quite simple. In order to complete the puzzle, you must fill each square with a number between 1 and 9 such that every row, column and 3x3 box on the board contains the numbers 1 through 9. Stated another way, you must fill each square such that no number appears twice in the same row, column, or 3x3 box.

These two different ways of looking at the puzzle are two of the principle ways players think as they play. On the one hand, you ask yourself, “How can I fit all the numbers in this box?” On the other hand, you ask yourself, “What numbers can fit in this square without causing a conflict with other numbers in the same row, column, or 3x3 box?”

In spite of the simplicity of the game, Sudoku puzzles can vary widely in their difficulty. Sudoku allows you to select the difficulty of the puzzle you want to play. By default, it will begin with easy puzzles and gradually increase the difficulty of puzzles as you improve.

2. Getting Started

2.1. To Start Sudoku

You can start Sudoku in the following ways:

Applications menu

Choose Games  ▸ Sudoku.

Command line

To start Sudoku from a command line, type the following command, then press Return:

gnome-sudoku

2.2. When You Start Sudoku

When you start Sudoku for the first time, you will see the puzzle selector screen, where you can choose the difficulty of the puzzle you want to play. If you've played before and have any unfinished puzzles, you can select those puzzles from this screen as well.

In the puzzle selector screen, the difficulty of the puzzle is displayed. The color surrounding the puzzle image corresponds to the difficulty. A dark red puzzle is harder than a light red puzzle, for example.

Double click on the puzzle of your choice to start playing.

Figure 1 Starting Sudoku

You can change puzzles at any time by pressing New. This will bring you to the puzzle selection screen, where you can select whatever puzzle you like.

3. Basic game play

To play the game, start filling numbers 1-9 in the squares such that no row, column, or 3x3 box has any number more than one time.

You can fill a number in a square with the keyboard or the mouse.

Keyboard

Use the arrow keys or the mouse to select the square you would like to fill. Then type the number you want to put in the square. Typing Backspace will remove the number.

Mouse

Click on a square to select it, then click in the center of the square to bring up buttons with the numbers 1-9. Click on a number to select it, or click on clear to clear the square. You can also double-click in the center of a square to bring up the number buttons.

If you enter a number that is in conflict with other numbers on the grid, the conflicting numbers will be highlighted in red.

Figure 2 Error highlighting

4. Saving and Resuming Games

Sudokus are saved automatically every few minutes and whenever you change games or close the application.

Figure 3 Resuming old games

Whenever you start Sudoku or click New, your saved games will be listed in the puzzle selection screen. You will see a miniature image of the saved puzzle, the date you last played it, and how long you have played it for. To open the puzzle, just double click on it.

If you'd like to stop playing one game and begin another, just select New and begin your new game.

5. Features

GNOME Sudoku provides a number of features that help you play puzzles.

Notes

Notes or Pencilmarks let you take notes in each square. Many players use notes to track possible values for squares.

Hints and Auto-Fill

You can use hints and auto-fill to have GNOME Sudoku tell you about possible values for a square or automatically fill in a square for you.

Highlighting

In highlighting mode, the current row, column and box are highlighted in different colors to make scanning the board easier.

Trackers

Trackers make trial-and-error solutions easier to keep track of. When you track a set of moves, the numbers are entered in a special color to help you distinguish those moves from moves made earlier in the game.

5.1. Taking Notes

To write notes (also known as “pencilmarks”) in a square, first select the square with the keyboard or mouse. Then, do one of the following:

  • Click in the upper region of the square (the region is highlighted with a square when you move the mouse over a selected square).
  • Type N

This will bring up a field in which you can type your notes. Type Return when you are finished editing your note.

You can also take notes in the bottom of the square by clicking in the bottom of the square or by typing M. However, this area is used when you ask for a hint, so you should not use this area for your own notes if you also plan to use hints.

You can clear the notes at the top of the square by typing Alt-N and at the bottom of the square by typing Alt-M.

You can add a number to the notes at the top of the square by typing Ctrl-1 through Ctrl-9 and remove a number from the notes by typing Alt-1 through Alt-9.

5.2. Hints and Auto-Fill

The Hint and Fill features work based on the logical possibilities given the current board. They do not work by looking at the solution. If you have made an error in an earlier move, these features may fill in or suggest incorrect values.

5.2.1. Hints

GNOME Sudoku can give you hints based on your current board. You can ask for a hint for the currently selected square by clicking hint, selecting Tools ▸ Hint, or typing Control-H. This will put a list of possible values in the bottom of the square.

Figure 4 Hints

If you want to remove or alter the hint, you can edit the text by clicking in the bottom of the square.

For very difficult puzzles, you can choose to have Sudoku show you the possible values for all squares. To turn this mode on, toggle Tools ▸ Always show hint. Note that this can make easy puzzles too easy, so you should use this mode sparingly.

Figure 5 Sudoku in Always-Show-Hint Mode

5.2.2. Fill Square

To automatically fill in a square for which there is only one possible value, you can click Fill, select Tools ▸ Fill, or type Control-F. This is useful, for example, when you have filled in 8 or 9 squares in a row and want to quickly fill in the last empty square.

If there are more than one valid value for the entry, nothing will happen.

5.2.3. Fill All Squares

You can automatically fill in all squares for which there is logically only one value at the moment. To do so, select Tools ▸ Fill all squares, or type Control-A.

This feature should only be used to help you when you are very stuck on a difficult game. Using this feature on an easy game can solve the entire puzzle in one click, resulting in a very boring game!

5.3. Highlighting

You can turn on highlighting to automatically highlight the current row, column and box in different colors. This can make it easier to see which values cannot go into a current square. To toggle highlighting, you can:

  • Click Highlighter
  • View ▸ Highlighter
Figure 6 Sudoku with highlighting

5.4. Trackers

You can use trackers to keep track of multiple moves at a time. Tracked moves will be entered in a different color to make them visually distinct. You can also delete all tracked moves at one time. This is particularly useful for solving difficult puzzles by trial-and-error.

Some sudoku players believe you should never use trial-and-error to solve a puzzle. These players should not use this feature.

You can toggle the tracker-interface by doing one of the following:

  • Tools ▸ Track additions
  • Click Track additions

This will bring up a list of trackers on to the right of the current game. Create a new tracker by clicking Add Tracker. From this point forward, any number you enter will be part of the selected tracker.

You can clear all the values that are part of a tracker by selecting the tracker from the list and clicking Clear Tracker. You can clear all values that are not part of a tracker by clicking Clear Others.

6. Printing Sudoku

GNOME Sudoku can print games for you to play on paper. This is useful if you have to leave the computer but want to finish a game you have started, or if you want to print out a bunch of puzzles to do later.

To print the puzzle you are in the midst of playing, click Print or select Game ▸ Print. This will include the numbers you have already filled in.

To print blank puzzles, select Game ▸ Print multiple sudokus.

You will then see a print dialog that lets you choose how many games you would like to print and how many games you want to print on each page (the more games you print per page, the smaller the games will be).

You can also select the range of difficulty you want the games to be in. The games will print in order of difficulty from easiest to hardest.

To create a 25 page mini sudoku book for yourself, you could select to print 100 sudokus, at 4 sudokus per page, with games ranging from easy to hard.

Figure 7 Printing a Mini-Sudoku book from Sudoku

By default, Sudoku will not print games that you have already played. If you're printing out games for a friend, or if you don't care about repeating games, you can check Include games you've already played in list of games to print.

You can also hand-select the games you would like to print by expanding the Games List and selecting multiple puzzles on the list.

7. Known Bugs and Limitations

7.1. Limited Puzzle Statistics

GNOME Sudoku ranks puzzles based on the number of squares that can be rapidly filled. The puzzle statistics box shows you the overall rating and shows you three pieces of information:

  • The number of squares fillable by elimination, starting from the blank grid (i.e. only a 2 can go in this box, so it must be a 2).
  • The number of squares fillable by filling, starting from the blank grid (i.e. only only one square in this row can be a 2, so it must be a 2).
  • The number of times in solving the puzzle that the computer had to use trial-and-error, or “guessing”, to solve the puzzle.

Many users are upset to know that the computer solver uses trial-and-error, especially since some Sudoku gurus say you should never guess to solve a puzzle. There are a number of other algorithms that can be implemented to help the computer solve sudoku, such as the swordfish and X-wings patterns.

At present, Sudoku only uses the two algorithms described above as well as trial-and-error. When the statistics box says that Sudoku needed to use trial-and-error X number of times, it does not mean that a human would have to use trial-and-error to solve the puzzle.

8. About Sudoku

Sudoku was written by Tom Hinkle (). Sudoku is now part of GNOME games.

To report a bug or make a suggestion regarding this application or this manual, see the Feedback section of the GNOME User Guide.

This program is distributed under the terms of the GNU General Public license as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. A copy of this license can be found at this link, or in the file COPYING included with the source code of this program.

  • Sudoku Manual