Today (2019 July 6) a new user had posted a question that received some upvotes Given $N$ integers on a circle, how to choose them in pairs to obtain minimum sum? and I had provided an answer that didn't solve the problem.
Now the PO has deleted that question and I wonder, how that is possible because if I remember right, questions that have an answer can't be deleted.

So my question is what the rules are for deleting one's own question if it has received answers, also in respect to the people who put effort in contributing to the solution of problems by providing answers and participating in discussions.

Edit (YCor) Here's the chain of events at this time (time GMT with missing minutes which I don't have access to); please further edit to improve it if necessary:

• July 6, 9:00 question posted by OP (user Shrijana)
• July 6, 12:00 answer posted (by OP of this meta post); discussion related to the question in the comments
• July 6, 16:00 question deleted by OP
• July 6, 16:30 this meta post
• July 6, 21:00 question undeleted (3 votes)
• July 7, 2:00 one user mention that a duplicate was posted and deleted (then mentioned by another user that it was deleted by OP)
• July 7, 8:30 one user mentions link showing that it's an ongoing (July 2019) contest (as was previously suspected in comments). This was then mentioned in the question as a warning
• July 7, 9:00 this user vandalizes the question (by erasing all the mathematical contents of the question) and its title (with edit approval) and requests deletion by moderator