Inspired by a question in chat from a new user, I thought it would be a good idea to have a tag for challenges where the output is a truthy value if the input meets certain criteria, and falsey otherwise. would make a good tag name - it's precisely what these types of problems are called in computer science.

Some examples of challenges where this tag would be relevant:

  • 4
    \$\begingroup\$ Yes please, I've been thinking about adding that tag for ages. \$\endgroup\$ Commented Nov 14, 2016 at 19:30
  • \$\begingroup\$ A couple of my own challenges this would apply to: 1, 2, 3, and 4. \$\endgroup\$
    – DJMcMayhem
    Commented Nov 14, 2016 at 19:40
  • \$\begingroup\$ @DrMcMoylex I'm pretty sure whoever creates this gets an instant Taxonomist, and the tag badges will probably also be unlocked immediately. ;) \$\endgroup\$ Commented Nov 14, 2016 at 19:56
  • \$\begingroup\$ If nobody objects to the proposal, I'll create this tag in a few hours. \$\endgroup\$
    – user45941
    Commented Nov 14, 2016 at 20:16
  • \$\begingroup\$ Should questions where there are multiple boolean outputs count? If so, codegolf.stackexchange.com/questions/61175 \$\endgroup\$
    – Blue
    Commented Nov 15, 2016 at 19:45
  • \$\begingroup\$ @BlueEyedBeast For that one, I'd say yes (it's really two decision problem challenges rolled into one). \$\endgroup\$
    – user45941
    Commented Nov 15, 2016 at 19:46
  • \$\begingroup\$ Love this idea, thanks for featuring my question, and editing in the tag for me :) \$\endgroup\$
    – FlipTack
    Commented Nov 19, 2016 at 14:42
  • \$\begingroup\$ A mod could probably tag this as [status-completed]. \$\endgroup\$
    – mbomb007
    Commented Dec 6, 2016 at 14:58
  • \$\begingroup\$ @mbomb007 Not until all of the existing challenges get tagged \$\endgroup\$
    – user45941
    Commented Dec 6, 2016 at 16:53

2 Answers 2


Mego created the tag. Feel free to propose an edit to the tag wiki if you think it can be improved.

Now comes the tedious part: identifying challenges that fit the tag, and (slowly - we don't want to flood the front page) adding the tag to them. Below is a list of challenges to which the tag needs to be added. If you come across any challenges not listed here, please add them to the list. If you add the tag to any challenge listed here, please remove it from the list.

I (Mego) will be adding the tag to 5 challenges per day, to limit the number of older challenges being bumped to the front page. Please refrain from large amounts of tag edits at once.

(the list is currently empty - please add more if you find them!)

  • \$\begingroup\$ Would you consider this challenge a decision problem? It's very close, the only problem is that there are three distinct outputs, and the output format is a little more restrictive \$\endgroup\$
    – DJMcMayhem
    Commented Nov 17, 2016 at 3:52
  • \$\begingroup\$ @DrMcMoylex I'd say that's more classification than decision problem. \$\endgroup\$
    – user45941
    Commented Nov 17, 2016 at 13:10
  • \$\begingroup\$ Similar thing here. We probably need to stick to two possible outputs, or else everything would end up being a "decision problem" \$\endgroup\$
    – Luis Mendo
    Commented Nov 18, 2016 at 13:44
  • 1
    \$\begingroup\$ Here's how I see the distinction: a decision problem is about deciding whether or not an input meets a certain set of criteria. Classification is about classifying an input - deciding which of multiple sets of criteria the input satisfies (if any). They're similar, but the difference is that a decision problem is a yes-or-no question. \$\endgroup\$
    – user45941
    Commented Nov 18, 2016 at 20:23

I'm not trying to argue either way, but since this is ...

Why? You say that you think it would be a good idea, but you don't explain what you think the benefit would be. The purpose of tags is to serve as a kind of recommendation system: "If you liked that question, you might like this one", or conversely, "I you don't like that question, you probably won't like this one".

Is being a decision problem really an attribute which people care about when deciding which questions to answer or avoid?

  • \$\begingroup\$ Based on the chat message that prompted this proposal and the comments on it, yes, people do want to be able to search for this attribute in challenges. \$\endgroup\$
    – user45941
    Commented Nov 14, 2016 at 20:30
  • 1
    \$\begingroup\$ Fair enough. Maybe you should edit a quote into the question. \$\endgroup\$ Commented Nov 14, 2016 at 20:34
  • \$\begingroup\$ There's already a transcript link. That's plenty, in my opinion. \$\endgroup\$
    – user45941
    Commented Nov 14, 2016 at 20:35
  • 7
    \$\begingroup\$ Since I'm the user who's linked to in the OP, I feel I should weigh in. For reasons I can't totally pin down, I'm fascinated by these questions. I think it's because of the simplicity of the specs, the rigorous and inarguable ways to prove if a response complies, and most importantly the golfing potential. Some of the best responses I've seen on this site have been on these style of questions. They seem, in my view, the 'purest' form of code-golf. Here's an input, you need to produce a true or false output. It's as simple as that, and I actively seek out these questions over any others. \$\endgroup\$
    – FourOhFour
    Commented Nov 14, 2016 at 20:54

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