One of the rules in the weekend event I run - the MathsJam - is that you are not allowed to stop people from enjoying themselves. This is not rigorously enforced, people just buy into it. A consequence is that if people are enjoying a puzzle, and you get the answer, you don't share it immediately.

If it really matters to you then you can write down the solution so others will know you got it first, but most people don't care about the credit, they just love the sharing of puzzles and other fun stuff.

It doesn't seem to work online - there are always those who insist on "sharing" just how clever they are.