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The index page for all Programs on the site?

The DFF Play CD?

Zipped file DFF Play contains  executable version of about  75 of the 200+ programs from the site, mostly those I particularly liked or thought would be of widest interest for non-programmers.  The file is rather large, about 20mb..

Anything else?




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Not a programmer (yet)?

 That's OK -  the executable version for any puzzle or  game you find here is available for download.  Just scroll down to the bottom of most any description page and you'll find a "Download executable" link. Downloaded programs are in "zipped" format to reduce size and may require an "unzipper" program unless you are running Win XP or later.  Here's a link to a free one. 

Check  out  the Most Popular  Downloads from DFF   (updated weekly)

First time visitor?

Take a look at the Introduction page to see what this site is about

Notes for Teachers


What's New


January 28, 2016:  It did not take long to recognize the need for for the first two enhancement suggestions in last week's HowManySquares program.    HowManySquares Version 2 adds the ability to view remaining squares after each move or on request. Also grids can now be saved and restored.   Both features are helpful when working on larger grids.  So far I've solved (and saved) up 7x7 grids.  Still working on 8x8.     

January 20, 2016:

There are 30 squares of all sizes in a 4x4 grid of 40 matchsticks. "What is the minimum number of matchsticks that need to be removed  to leave no squares of any size?"

How many Squares? investigates this problem, from  the  latest addition to my library of math & puzzle books: Challenging Math Problems, Terry Stickels, Dover Publications, 2015

Program users can investigate various grid sizes and work on solving by clicking to add or remove matchsticks with feedback along the way.   For those with a little mathematical curiosity, there are some interesting relationships across grid sizes among the number of matchsticks, the number of squares, and the minimum number of sticks to eliminate .  

January 2, 2016:

OK, holidays are over; back on the diet and back to "work" programming.  Being known to the family as a puzzle lover, I received one called "Aristotle's Number Puzzle" for Christmas this year - nothing to do with Aristotle as far as I can tell. It's a hexagon shaped board made up of of 19 hexagon shaped tiles numbered 1 through 19.  The objective is to arrange them into a "magic" hexagon in which values in every horizontal and diagonal row (15 in all) sum to 38.  Our "Brute Force" program can find the 12 variations of the solution by defining 15 equations representing sums for the 19 variables . These are all isomorphic versions of the single solution, i.e. they represent rotations and mirroring of the solution. I decided to investigate further, starting by posting a Delphi Techniques program to draw Hexagonal Boards of various sizes. Here's one with puzzle hints filled in.     

January 1, 2016:  Happy New Year to all!

December 24, 2015:Merry Christmas!

We are just back from 10 wonderful days in Central Europe (the  Prague, Vienna, Budapest triangle) with family.  None of these will replace Lauterbrunnen, Switzerland as our favorite, however it was worthwhile and educational none the less.   We had been to Vienna many years ago but the others were first-time visits.   Both Prague and Budapest have similar geography; straddling a river with a castle on the high ground on one side and the peons living on the other side.  Both were occupied before and after WW2; first by German Nazis, then by Russian Communists.  Lots of differences in the details though.  All  three cities have large Christmas Markets where the girls spent many hours buying gifts and souvenirs while the guys sampled and compared beers, wines and brandies (e.g. Palinka in Budapest - ouch!).   Just spending time with our wide-spread family was the real highlight for me.  The children and older grandchildren are experienced travelers by now, so Grandma and I could mostly just relax and  enjoy.     

In Vienna we had a long lunch with Cristian Kranich after attending a performance of the Spanish Riding School Lipizzaners.  Christian graciously tested the "stay as long as you want" tradition of the Vienna coffee house by occupying an 8 person table alone at the classic Café Central  for several hours before we arrived, bypassing the long line of those awaiting a table.  He is an interesting fellow who is using some of my code in his hobby of analyzing Eastern and Indian flute scales.   He programs and designs/builds hardware for a niche market and is the closest to a true polymath that I have ever encountered.   Thanks for the hospitality Christian!  


As the final posting this year, here is an unpolished version of my Rectangle in Polygon program started in October.  The idea is to to find the largest  area rectangle that can be inscribed in an arbitrary convex or concave simple polygon.  (Simple==>sides do not cross.)   A fun and challenging project that still needs some fine tuning for efficiency. 


December 4, 2015: Between travel and  that Holiday at the end of the month, December will be a sparse programming month for me.  I did receive an interesting email recently from a scout troop leader which is just the kind that makes my week.  The troop built a catapult based on the a page actually provided by another viewer several years and available from my Catapult Simulator page.   Here's the email:


Building a catapult is one of the requirements for the engineering badge or the Arrow of Light, the only cub scouts achievement that can be worn on the boy scout uniform - so the Webelos 2 (older boys) in our cub scout pack in middle Tennessee had high enthusiasm for this project.

We downloaded the parts list and the pictures from DFF's "A Catapult Story" and the boys built it pretty much according to the instructions and pictures in an assembly line - one boy measured and marked the PVC, another cut the marked pieces, another   labeled the pieces, and another did a dry assembly (see picture). After we made sure it all looked good assembled, it was disassembled, PVC adhesive applied to the ends of the pieces, and reassembled (we used the sawed-off bottom of a movie theater cup for the cup). Using PVC adhesive was faster than screwing in all the pieces, as was done in the instructions - the entire catapult was cut and assembled in about an hour (easily done in one den meeting). The only other difference is that we used threaded rod for the stop - it worked, but you can see in the animation that it bends when the arm hits it. 
The boys attached streamers to the back of the projectile, so they could more easily see it in the air - you can see the tails in the launch, below. It easily gets 20 feet of height and 60 feet of range. Worked beautifully, and the kids loved it - thank you very much!
- James W, den leader





November 27, 2015:  

Our "Wordsearch" program allows users or the program to solve those "straight line" or  "crooked path" problems.  Crooked path problems could not revisit letters within a word, until today.  Word Search  Version 2.1 adds a "Revisit OK" checkbox to enable solving  the recent Mensa Brain Puzzlers Calendar for November 21. Here's the puzzle: Start on a letter and move horizontally, vertically, or diagonally from letter to adjacent letter to spell out a two-word famous fighting force. You may return to a letter and reuse it. All the letters will be used at least once.

November 13, 2015:


6th grade Algebra?

 Brute Force is our  program which solves many algebra based puzzles with integer solutions. It works by exhaustive search over a set of values, trying all combinations in a set of equations.  A viewer recently reported having a problem solving this equation set which he described as a "6th grade level algebra problem".   Not in my 6th grade!   In any event, the program couldn't find a solution with a trial digit range from 1 to 30.  That is, until I increased the maximum number of trial digits from 20 to 50.   Brute Force Version 3.4.1 posted today implements the change and finds the solution 5 seconds!  It now also warns if you specify a range larger than 50 numbers,  Sample problem Test50.prb is the  problem that uncovered the bug and is included in the downloads.   I'm off to try my high school solving skills on this problemJ.


November 12, 2015:  At least for me, Microsoft made the Windows file search option virtually unusable when they rewrote it for Windows 7.    It's a function that I rarely need, but when I do, I don't want to search help or the internet to find how to do it.  This week, I finally wrote a FastFileSearch program to find files meeting masking criteria from a selected start folder (e.g. find *permut*.exe to list all permutation related programs in my DFF folder).   No content searching yet, but that enhancement is in the wings if I need it.  Maybe Windows 10 search will work, but when last I checked ,the Win10 Edge browser did not support  add-ons and the Win32Help program could not be installed.  Both of those deficiencies are deal breakers for me.           

October 29, 2015:

Last Sunday's Mensa Calendar Puzzle led me to dig out the Self Describing Sentences program written several years ago.  Sure enough it can solve this one, but I can't revisit a program without finding some bug or desired enhancement.  This time I added the ability to count the number of consonants in a self describing manner.  Self Describing Sentences Version 2.3 was posted today.  

November's big project is a program to approximate the largest rectangle that can be drawn inside of an arbitrary polygon.   A patient user requested it a few months ago and it does sound like an interesting challenge.  

October 19, 2015: 

Complete this grid with 10 different words using the given letters

I recently discovered the was a perfectly good name already defined (Double Word Squares) for  what I had been calling "Square Word Grids" to distinguish them from the symmetrical "Word Squares" puzzles.    Double Word Squares Version 3  posted today has several major enhancements and has occupied my spare time for the past 8 weeks!  I will admit that the "fun level" decreased during the period and I reverted to "never give mode" several times.  The resulting product still needs polishing, but I believe that it mostly works.  Please let me know if you find otherwise.    The changed and new features include a revised search algorithm and revised user interface.  It now takes less than a second to solve this Mensa Puzzle which the previous version could not solve in over 10 hours of run time! 

October 2, 2015: 

Late last year, curiosity led me to investigate how license keys  or serial numbers might be created.   Activation procedures requiring name, email address or other personal information lead me to believe that the assigned key contains data used for verifying that the user is the owner.    A user recently uncovered a couple of bugs when a larger number of fields or special characters are included.  License Key Demo Version 1.2 corrects these and a couple of others discovered during testing, 


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