A combination challenge takes multiple other challenges and combines them. For example, this challenge combines the challenges of finding the Greatest Common Divisor (GCD) and Prime Factorization.

Which of the following stances does the community take on such challenges? Assume that you are somehow able to tell 100% that one of the parts, if posted alone, would be a duplicate or not.

  1. A combination challenge is duplicate if and only if all of its parts are duplicate.
  2. A combination challenge is duplicate if any single part is a duplicate.
  3. A combination challenge is duplicate if and only if that exact combination challenge has been posted before.

New users viewing this post should be aware of the following posts that attempt to formalize what it means to be a duplicate on this site. These questions and answers do not necessarily reflect my personal views. Rather, they show what the community as a whole thought at the time. As usual, swing a vote the other way if you disagree, or post your own answer.

  • \$\begingroup\$ Even if all parts have been asked before, combining them may offer up new possibilities for approaching the individual task, as you don't necessarily need the exact same intermediate result (e.g. if the second task would undo some of the work of the first one). At the same time I could see cases where there are not many interesting options other than slapping the two winners of the duplicates in question together as a new submission. Read that as: I'm not sure what my opinion on this is other than "use your best judgement". \$\endgroup\$ May 12, 2014 at 16:55

1 Answer 1


The questions to ask here is: can the question be solved in a different way than the previous two challenges? Does it add anything interesting over them?

If someone posts a challenge that combines two algorithms, but there is one algorithm that does both things, then it adds something new and interesting, and it can be solved in a different way. So, it should be left open.

If the combined challenge can only be solved by combining the two seperating algorithms, then it does not really add anything interesting and it cannot be solved in a different way. So, it should be closed as duplicate.


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