What's New - May, 2012
May 3, 2012: Another avid logic problem solver managed to break my "Logic Solver" program last week, this time with a Geocaching problem with 10 different teams, home towns, and cache counts. The previous version would only handle 9 values per variable without burping, but Logic Problem Solver, Version 4.0 , just posted, handles up to 15 values and can solve the problem (also included in the download if you want to try your hand).
May 8, 2012: The CHOICE statement type was added to Logic Problem Saver Version 4.1 today after 5 days of challenging work. The full program is one of the most complex I've written, with about 6000 lines of code equally divided between handling the user interface and searching for a solution. It uses facts, and other logical relationships extracted from problem description text by the user. Choice statements simplify the user's job when we are told that a variable value is associated with 2 or 3 possible values of another variable. Such statements allows us to generate (negative) Facts about what values the associated variable cannot have. For example: If we know that "Bob lives either in Virginia or North Carolina" (the Choice statement), then he cannot live in any of the other states that the problem allows. Those negative facts (e.g. "Bob does not live in Florida") can help complete the "Truth tables" necessary to resolve who lives where. In the May 3rd Geocaching problem, the three Choice statements eliminate user entry of 24 of those negative Fact statements. Now if I can just find a dozen or so similar problems, I will have saved enough time to pay for effort of the enhancement. J
May 11, 2012: ClearBlankLines is a program which removes entirely blank lines from text files. It was written several years ago to solve a particular problem I had with generated html code on my website when some unknown action added 35,000 blank lines to web pages. The pages were still viewable but speed slowed considerably, required storage space increased, and my HTML editor program choked. I have had a surprising number of emails thanking me for the program since then for helping them resolve similar problems. Today's update adds an option requested recently by a user to also remove leading blanks from lines which contain text.
May 19, 2012: A Sudoku Helper program was posted last month which led to this week's project, generating random Sudoku puzzles. As usual, the problem turned out to be harder that I thought. Generating valid filled boards is relative easy, there are billions of them. The hard part is to remove some of the values and meeting the requirement that the board can be filled in only one way. Once 53 or so numbers have been randomly removed (28 clues), more than 99.8% of the resulting boards will have two or more solutions and the probability of a random unique solution decreases rapidly from there. It's still a work in progress, but Sudoku V3.0 posted today averages about 1 unique solution per 400 boards tested for random puzzles with 28 or more clues.
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