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Make printable 7x7 Sudoku-like puzzles
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Back in 2011, I found an open source Sudoku generator that can generate any size of Sudoku, with any pattern for the subgrids.

I used the generator to make a handful of 7x7 Sudoku-like puzzles for my blog.

Recently, I took an interest in this, and used the Java client to make a seven-page, 42 puzzle Sudoku book. The process was laborious: I used the Java program to make a puzzle, then I had to put multiple screenshots in an image for each page of the book using Gimp. It took me about two days to make a seven page book.

The purpose of this project is to make the entire process of making a 7x7 Sudoku puzzle easier.

To play

Open up the file example.pdf.

This puzzle is a variant of Sudoku I like to call "Prosperity 7". In this Sudoku variant, the board is only 7x7, and only the numbers from 1 to 7 are used. Neither 8 nor 9 are ever placed on this board.

The object of this puzzle is to place the numbers 1 through 7 in the blank spaces such that:

  • Each row only has one instance of each number between 1 and 7. In other words, no number is duplicated in a given row.

  • Each column only has one instance of each number between 1 and 7. In other words, no number is duplicated in a given column.

  • Each of the seven-square shapes bordered by thick lines have all of the numbers between 1 and 7 precisely once.

The puzzles in example.pdf are sorted by difficulty, starting with easier puzzles and moving up to hard puzzles.

To generate PDF files

Have Python (either Python2 or Python3; the script is a polyglot) installed.
Ideally, use a virtual environment. Then:

pip install -r requirements.txt
./ puzzle.pdf puzzles/*.xml 

Of course, one does not simply run pip install -r requirements.txt and have everything work without problem. There are various development libraries which need to be installed, but they are standard libraries available for the system with both Cygwin and CentOS 7; the libraries that need to be installed include cairo, pixman, png, pango, and poppler.

The first argument for the script is the PDF file generated.

The subsequent arguments are files which are generated by the Java program in the Generator/ directory (to get one started, I have included a number of already generated puzzles in the puzzles/ directory).

It is also possible to use the script to only look for duplicate puzzles:

./ dupcheck puzzles/*.xml

Generating more puzzles

To generate more puzzles, we need a Java interpreter. Both Oracle Java 8 and OpenJDK 1.8.0_191 (i.e. the OpenJDK included with CentOS 7) work with the supplied jar file which generates the puzzles in batch mode.

To run the puzzle generator, make sure to be in a GUI environment (X windows, Windows 10, etc.) and run the following commands:

cd Generator/

This will run the Java generator in batch mode. It will take about two minutes to generate 204 puzzles. The generated puzzles will be in a directory called Puzzles/; to make a PDF file:

cd Generator/
cd ..
./ output.pdf Generator/Puzzles/*xml

Generating puzzles by hand

In a GUI environment with Java installed, double clicking on the Sudoku-NPGeneratorV2_0_2.jar file in the Generator/ directory should open up a generator. With a command line, it would be:

cd Generator/
java -jar Sudoku-NPGeneratorV2_0_2.jar

At this point a GUI window will open with the Sudoku generator. Do the following to generate a puzzle:

  • Select File -> Open File
  • Open the file Prosperity-7-template.xml
  • Click on the button Set near the bottom of the window
  • Click on the button Generate
  • Click on the button Play
  • Select File -> Save file
  • Choose a unique filename for the file
  • Click on Save

To the right of the button Answer, it shows how hard the puzzle is (the more "points" a puzzle has, the harder it is to solve)

It's possible to change where we put number hints (one can observe a number of different patterns for hints in the example.pdf file supplied here): After opening up the Prosperity-7-template.xml file, click on Set then right click to add or remove blue squares (squares were we put number clues in a puzzle).

Note that in order to print, the puzzle .xml files need to be 7x7 files using the same block arrangement (same set of heptominoes used the generate the 7x7 square). The PDF generator can handle different location for the number hints; it can not handle a different arrangement of sub-blocks nor a different puzzle size (the PDF generator will refuse to print incompatible files).

Installing the Caulixtla008 font

While the puzzles look perfectly fine using the Weasyprint default font, one can optionally install the Caulixtla008.woff font. See this page for notes:

Example #1 (Windows + Cygwin, should work elsewhere):

mkdir ~/.fonts
cp Caulixtla008.woff ~/.fonts

Example #2 (CentOS 7 system-level install):

mkdir /usr/share/fonts/Caulixtla008
cp Caulixtla008.woff /usr/share/fonts/Caulixtla008/
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