Deduplicate - Find elements in an array but not in the other

[hobovsky]

From #39

1. Remove All The Marked Elements of a List

   • 7 kyu
   • Accepts O(m * n) solutions. JS setup is completely botched.
   • Satisfaction 89% with 8700+ completions.
   • No pending issues
   • 10 languages + 1 pending translation
   • Published Oct 2015, author active.

2. Array.diff

   • 6 kyu
   • Accepts O(m * n) solutions.
   • Satisfaction 88% with 232k completions.
   • 1 pending issue.
   • 23 languages + 6 pending translations.
   • Published Sep 2013, author active.

3. Array.diff hero

   • 5 kyu
   • Does not accept O(m * n) solutions, requires O(m + n).
   • Satisfaction 84% with 600+ completions
   • 2 pending issues.
   • 1 language (JS only), no pending translations.
   • Published Nov 2016, author inactive.

[hobovsky]

What's bad about all of the kata in this group is that none of them clearly defines what "remove" means: should one of the arrays be modified, or should inputs be left untouched, and a new array be returned? It's not specified, and not tested, in any of the discussed kata.

I think that the kata 1. should go away. It's a duplicate of 2. with additional terrible setup in some languages (and in JS it's plain broken).

I am not sure what to do with kata 2. and 3. I think it's not necessary to have both, and I would like to have only the "performance" version, but amount of languages of both differs wildly. Kata 3. is also spoiled with solutions already submitted to 2. I don't know what would be the best:

• keep both 2. and 3.?
• Retire 3. as spoiled by 2.?
• Retire 2. because dull and keep 3.?
• Retire 3., keep 2., and harden it to reject O(m * n) solutions?

[Blind4Basics]

• I'd like point 4, but I doubt it's doable for 23 languages...?
• otherwise, point 2, I guess

In any case, get rid of 1, yeah

[error256]

3:

Each element x in both arrays is integer and 0 ≤ x ≤ 25.

Increase array sizes so that more general solutions from the other katas time out?

[ejini6969]

Related to #152

[EloiseRosen]

vote for retire 1 and 3, keep 2