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# teukon/gist:16b6de379907bb2a3aa4 Secret

Last active Dec 3, 2018
Regex Golf - Unofficial Bonus Levels

### Regex Golf - Unofficial Bonus Levels

1. Subtraction Quantify with care.
2. Typist With apologies to Dr. Dvorak.
4. Anyway Old MacDonald had a farm...
5. Tic-tac-toe Don't forget the horizontals.
7. Matryoshka Pay attention to detail.
8. Euclid Greed is good.
9. Latin squares No mathematics; just logic and reasoning.
10. Dominoes Caution! Rabbit holes.

Each problem has a robust solution (can be done "without cheating"), unlike "A man, a plan", "Glob", and "Balance" from the original set. In each case, the pattern should be unambiguous. A solution to a problem is considered robust if it conforms to this pattern for any string matching the problem's domain regex:

Level Domain regex
Subtraction `^x+ - x+ = x+\$`
Typist `^[a-z]+\$`
Addition `^x+ \+ x+ = x+ \+ x+\$`
Anyway `^[a-z]+\$`
Tic-tac-toe `^[\.OX]{3} [\.OX]{3} [\.OX]{3}\$`
Modulus `^x+ % x+ = x+\$`
Matryoshka `^([a-z]+ )*[a-z]+\$`
Euclid `^gcd\(x+, x+\) = x+\$`
Latin squares `^[a-z]{4} [a-z]{4} [a-z]{4} [a-z]{4}\$`
Dominoes `^([0-6]{2} )*[0-6]{2}\$`

Please refrain from posting solutions here until the thread is well underway (20+ posts). Questions, total scores, and gentle hints are ok.

A warm thank you to Davidebyzero for helping me refine each of these problems, and for coming up with some brilliant solutions. Our testing and development notes can be found here and here (caution: spoilers).

### Davidebyzero commented Feb 22, 2014

 I've made a meta-post on xkcd forums, asking what subforum my actual post should go in. Note to people coming over to play this problem set: Please avoid posting your solutions here (maybe even avoid posting your scores) and instead, post them somewhere else with a link to them here, or post the md5sums of the solutions here. At least until the thread here has become long enough that even people with really large monitors won't be able to see the spoilers without scrolling down.