When answering a CNR challenge it's common to get the response: "Well done, but that was definitely not what I had in mind".

I feel like it should be perfectly fine for anyone to post a second crack if OP says the intended solution was substantially different. The first crack is of course still valid, but the challenge could still be a very interesting to others, since they know there are other, possibly more complicated, complex or obscure solutions.

I've never seen anyone posting a second crack, and OP often posts "The intended solution was: abcde. (I've done this myself quite a few times).

Can we encourage others to post a second crack to the cop post if there is a substantially different solution to it? This would also mean that Cops are discouraged to post the intended solution until the SAFE-date, even if it's already cracked.

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    \$\begingroup\$ What defines "substantially different"? \$\endgroup\$ Nov 13, 2016 at 13:38
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    \$\begingroup\$ If this is enabled, all future crackers would need to be marked as non-competiting, as it becomes too easy to game the system otherwise. \$\endgroup\$ Nov 13, 2016 at 13:43
  • \$\begingroup\$ "substantially different" can be subjective \$\endgroup\$
    – AlexRacer
    Nov 13, 2016 at 13:53
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    \$\begingroup\$ I don't think that "substantially different" is really that big of an issue. We basically do the same thing with code golf submissions. Each submission should be substantially different from each other. In code-golf, the one with fewest bytes wins, while in cops-n-robbers, the first one posted wins. \$\endgroup\$ Nov 13, 2016 at 13:59
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    \$\begingroup\$ "Substantially different" is of course subjective, and I have no proposal for a general rule. I agree that the first one "wins", but in my opinion, a crack that brings something completely new to the table deserves recognition (if posting it is accepted). If voters don't think a crack is "different enough" or not clever: Don't vote, or downvote. \$\endgroup\$ Nov 13, 2016 at 14:36

2 Answers 2


Sure, but by default, only the first crack should receive credit. This would keep it in line with our current policy, while allowing additional cracks (that would be non-competing). Challenge authors can override this default if desired.

  • \$\begingroup\$ I agree. The non-competing answers should of course be clearly marked as such. \$\endgroup\$
    – Zgarb
    Nov 13, 2016 at 14:50
  • \$\begingroup\$ I'm not a fan of cluttering a post with non-competing answers. I'd prefer this not be the default, so challenge authors have to specify this if they want it. \$\endgroup\$ Nov 14, 2016 at 23:13

In some cases the new crack could be more interesting or obviously more intended. But in other cases this could be too open-ended.

Instead, we should encourage the cops to fix their submissions and post new versions. If that couldn't be fixed, it fails to be a competitive cop answer, so it doesn't make too much sense to have more robber answers related to it either.

If we really want to allow the new robbers, we should find some ways to decide which answer is better, for example the shortest. Then we could allow posting competitive answers using different approaches in some challenges, or even give credit to better answers. But we shouldn't encourage subjectively "interesting" cracks. Specifically, we shouldn't encourage:

  • Guessing the original intention;
  • Accepting arbitrary restrictions made by the cop;
  • Adding "creative" (in a sense that doesn't really help cracking) cracks to a too weak cop.

At least we shouldn't vote for these reasons. Cracks with the first 2 features could be competitive, too, though. But most are not.

In any cases you can always post the supposedly better cracks in comments.


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