4 ms·

I like this regex, which divides a number by sqrt(2): (?=(x(x)).(?=\1$)\2+$)(?=(x\1)+(x?(x)))(?=\4(x(x?))\1+$)(?=.(?=(?=\4$)\4\5+$)(x?)(?=\3*$)(x?(

I like this regex, which divides a number by sqrt(2): (?=(x(x*)).*(?=\1*$)\2+$)(?=(x\1)+(x?(x*)))(?=\4(x(x*?))\1+$)(?=.*(?=(?=\4*$)\4\5+$)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\9))(?=.*(?=(?=\4*$)(?=\6*$)(?=\4\7+$)\6\5+$|$\4)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\13))(?=.*(?=\12\12\9$)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\17))(?*.*?(?=((?=\3*(x?(x*)))\21(x(x*?))\1+$)))(?=.*(?=\23*$)(\23\24+$))(?=.*(?=(?=\21*$)\21\22+$)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\27))(?=.*(?=(?=\21*$)(?=\23*$)(?=\21\24+$)\23\22+$|$\21)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\31))(?=.*(?=\30\30\27$)(x*?)(?=\3*$)(x?(x*?))(\1+$|$\35))(?=.*(?=\26\26)(?=\3*(x*))(\1(x)|))(?=.*(?=\34\34\40)(?=\3*(x*))(\1(x)|))(?=(?=(.*)\13\13\17(?=\6*$)\6\7+$)\44(x+|(?=.*(?!\16)\41|(?!.*(?!\38)\8).*(?=\16$)\41$))(\25\31\31\35){2}\43$)\20|xx?\B| Source: https://codegolf.stackexchange.com/a/198428 https://codegolf.stackexchange.com/a/198428

sph 2y ago
Very nice! Almost as complex as the regex to parse HTML: https://stackoverflow.com/a/1732454 https://stackoverflow.com/a/1732454
- Suppafly 2y ago
  Reminds me of work, a coworker was telling me that a new guy, who eventually quit, was really close to solving an issue with had with HTML in some fields where it doesn't belong, and then mentioned that the new guy was using regex to do it. I was like, I doubt he was actually close to solving the problem. That said, he likely would have solved our need because it really is just a subset of HTML used for stylizing text and not the full language, but it's a harder problem than people initially think.
  - sph 2y ago
    I figure he quit after the nightmares of backtracking regexes consuming the world started.
- tiagod 2y ago
  From the replies :) > In CS theory, regular languages are a strict subset of context-free languages, but regular expression implementations in mainstream programming languages are more powerful. As noulakaz.net/weblog/2007/03/18/… describes, so-called "regular expressions" can check for prime numbers in unary, which is certainly something that a regular expression from CS theory can't accomplish. – Adam Mihalcin Commented Mar 19, 2012 at 23:50
deleted 2y ago
[deleted]

I like this regex, which divides a number by sqrt(2): (?=(x(x*)).*(?=\1*$)\2+$)(?=(x\1)+(x?(x*)))(?=\4(x(x*?))\1+$)(?=.*(?=(?=\4*$)\4\5+$)(x*?)(?=\3*$)(x?(

sph 2y ago

Very nice! Almost as complex as the regex to parse HTML: https://stackoverflow.com/a/1732454 https://stackoverflow.com/a/1732454

Suppafly 2y ago
Reminds me of work, a coworker was telling me that a new guy, who eventually quit, was really close to solving an issue with had with HTML in some fields where it doesn't belong, and then mentioned that the new guy was using regex to do it. I was like, I doubt he was actually close to solving the problem. That said, he likely would have solved our need because it really is just a subset of HTML used for stylizing text and not the full language, but it's a harder problem than people initially think.
- sph 2y ago
  I figure he quit after the nightmares of backtracking regexes consuming the world started.
tiagod 2y ago
From the replies :) > In CS theory, regular languages are a strict subset of context-free languages, but regular expression implementations in mainstream programming languages are more powerful. As noulakaz.net/weblog/2007/03/18/… describes, so-called "regular expressions" can check for prime numbers in unary, which is certainly something that a regular expression from CS theory can't accomplish. – Adam Mihalcin Commented Mar 19, 2012 at 23:50

deleted 2y ago

[deleted]