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clues from a filled grid, was using the algorithm - loop over the whole grid looking for a clue (or symmetry group of clues) which can be safely removed - remove it - loop over the whole grid again, and so on. This was due to my vague feeling that removing one clue might affect whether another can be removed. Of course this can happen - two clues can be alternative ways of deducing the same vital fact so that removing one makes the other necessary - but what _can't_ happen is for removing one clue to make another _become_ removable, since you can only do that by _adding_ information. In other words, after testing a clue and determining that it can't be removed, you never need to test it again. Thus, a much simpler algorithm is - loop over the possible clues (or symmetry groups) _once_, in a random order - for each clue (group), if it is removable, remove it. This still guarantees to leave the grid in a state where no further clues can be removed, but it greatly cuts down puzzle generation time and also simplifies the code. I am a fool for not having spotted this in three and a half months! [originally from svn r6160]
This is the README accompanying the source code to Simon Tatham's puzzle collection. The collection's web site is at <http://www.chiark.greenend.org.uk/~sgtatham/puzzles/>. You should find several Makefiles in the source code: - `Makefile' should work under GNU make on Linux, provided you have GTK installed to compile and link against. It builds GTK binaries of the puzzle games. - `Makefile.vc' should work under MS Visual C++ on Windows. - `Makefile.cyg' should work under Cygwin / MinGW. With appropriate tweaks and setting of TOOLPATH, it should work for both compiling on Windows and cross-compiling on Unix. - `Makefile.osx' should work under Mac OS X, provided the Xcode tools are installed. It builds a single monolithic OS X application capable of running any of the puzzles, or even more than one of them at a time. Many of these Makefiles build a program called `nullgame' in addition to the actual game binaries. This program doesn't do anything; it's just a template for people to start from when adding a new game to the collection, and it's compiled every time to ensure that it _does_ compile and link successfully (because otherwise it wouldn't be much use as a template). Once it's built, you can run it if you really want to (but it's very boring), and then you should ignore it. DO NOT EDIT THE MAKEFILES DIRECTLY, if you plan to send any changes back to the maintainer. The makefiles are generated automatically by the Perl script `mkfiles.pl' from the file `Recipe'. If you need to change the makefiles as part of a patch, you should change Recipe and/or mkfiles.pl. The manual is provided in Windows Help format for the Windows build; in text format for anyone who needs it; and in HTML for the Mac OS X application and for the web site. It is generated from a Halibut source file (puzzles.but), which is the preferred form for modification. To generate the manual in other formats, rebuild it, or learn about Halibut, visit the Halibut website at <http://www.chiark.greenend.org.uk/~sgtatham/halibut/>.