Is a regex answer valid if it gives the reciprocal of the required output? [duplicate]

Question

This answer gives the reciprocal of the required output, rather than the required output itself.

In a simpler challenge this might cut out a significant part of the work, but for this particular challenge the bulk of the work is still being done. However, this still gives the answerer an advantage over a competitor using the same language but giving the correct required output.

As pointed out in a since deleted comment, the limitations imposed by pure regex mean that answers generally take unary input and give unary output (where arithmetic is required), which doesn't allow an obvious way of giving a fraction as an output, which the challenge in question requires. I think the compromise found, of using unary to express a reciprocal, is ingenious, but I'd like to see discussion of whether this is valid, so we can have consensus one way or the other.

Is such an answer valid?

Answer 1

Ask the OP

There are many ways to take input and return output. We've made some standardized ways so that challenges don't have to redefine them every time.

However, for stuff like printing the reciprocal, this is something the OP needs to decide. I don't think it is a stretch of the imagination to think that this could be abused on simpler challenges.

(In essence, the answer here is "no". This isn't an allowed default output format. OP can always override, and for this particular challenge, I'd personally vote to allow it)

Answer 2

Outcome for the specific challenge mentioned

I have reconsidered the output requirement following a comment from Neil on the answer in question:

@trichoplax Could you consider the answer as being the ratio of lengths of two specific capture groups? (This would actually make the answer shorter as it takes the trouble to make the whole match be the result.) – Neil

As a result, I have amended the output requirement:

So for input 8, both 1/8 and 0.125 are acceptable outputs. Output as separate numerator and denominator is also acceptable, to be inclusive of languages that support neither floats nor fractions. For example, 1 8 or [1, 8].

Answer 3

Call the input a natural number \$n\$. I don't see a qualitative difference between:

• Returning one number, in a challenge where it so happens that the reciprocal of the correct output is always infinity or a natural number \$≤n\$
• Returning two numbers \$(a,b)\$, to represent a fraction \$a\over b\$ where the numerator and denominator are both guaranteed to be \$≤n\$
• Returning two numbers \$(a,b)\$, encoding \$an+b\$, to represent a natural number that is guaranteed to be \$≤n^2+n\$
• Returning three numbers \$(a,b,c)\$, encoding \$an^2+bn+c\$, to represent a natural number that is guaranteed to be \$≤n^3+n^2+n\$
• Returning four numbers \$(a,b,c,d)\$, encoding \$(an+b)\over(cn+d)\$, where the numerator and denominator are guaranteed \$≤n^2+n\$
• Returning two numbers \$(a,b)\$, encoding \$a×2^{b-\lfloor {n/2} \rfloor}\$ (floating point)
• Returning four numbers \$(a,b,c,d)\$, encoding \${a\over b}+{c\over d}i\$ (complex rational number)
• Returning four numbers \$(a,b,c,d)\$, encoding \${a\over b}+{c\over d}\pi\$
• Various combinations thereof, and beyond

So the options are:

1. Consider each of the above to be a distinct language, following the established PPCG convention regarding command-line parameters. The N-mover answer would then be unchanged, except perhaps to call the language something like "Regex (ECMAScript, reciprocal output)".
2. Represent this metadata in some standard format (with the number of each backreference, and what it represents – \0 could indicate the return match itself), and add it to the byte cost of the regex. Then this would be a new language, focusing on pure regexes and confining the metadata format in a way that honors that restriction.