Can participation in online academic competitions destroy patent rights?

I am not familiar with details of UK patent laws, however, here in the US, you would probably be risking your right to obtain a patent. According to 35 USC 102(a)(1), one can obtain a patent UNLESS.... it has been in public use before filing a patent application.......In the US, there is a one (1) year grace period, that is, if you file your patent application within one (1) year of the public use, you can still obtain a US patent, but I do not believe that that is the case in other countries where you would seek patents from those countries.

Yes.
The filing date of the patent application, or priority date of an ealrier priority-founding application, stops the clock, well calendar, with regard to relevant prior art. In Europe and UK, there is no US-like grace period.
Although it may be argued that you did not make availabe any details, the outlined action weakens your case!
Further, be aware that algorithms and software "as such" are excluded from patentability. Having said that, technical solutions employing algorithms/software are not excluded.
You should seek adivce from a patent attorney exprienced in the field of "software-implemented inventions".
Feel free to get in touch;-)
Kind regards & all the best