Back Doors and Magic Squares

humble_programmer · Posted: Sat Jul 04, 2009 8:58 pm Post subject: Back Doors and Magic Squares

After spending more time than I care to admit reading these forums, I still am completely ignorant of what is meant by "back doors" or "magic squares". I've seen both terms mentions mentioned multiple times--and there's a "too concise to be instructive" mention on Glenn's website--but no one has offered a good explanation of (a) what they mean, or (b) why they matter.

Anyone care to "counsel the ignorant"?
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daj95376 · Posted: Sat Jul 04, 2009 9:37 pm Post subject:

http://www.sudopedia.org/wiki/Backdoor

tarek · Posted: Sun Jul 05, 2009 6:41 am Post subject:

If you are using a specific set of solving techniques. a backdoor is the minimum number of guesses that will allow you to solve the puzzle using that specific set of techniques.

The backdoor can be of size 0 .... if you solve the puzzle entirely with your set of techniques.

There are now several examples of puzzles that have a SINGLES backdoor of size 3.

Just remember to specify the set of techniques next to the referenced backdoor & remember also that the backdoor size does not tell you how many backdoor combinations are possible.

tarek